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Secondary 2 · Mathematics
Arithmetic · Proportionality

Plans and Scale

Before you start, make sure you know: Length (Secondary Year 1)
Before you start, make sure you know: Area (Secondary Year 1)

A road map of Mexico with a scale of $1:250{,}000$. The floor plan of your room at a scale of $1:20$. A model of the Zócalo. They all use the same tool: a ratio that relates the drawing to reality. If you understand it, with a ruler and a drawing you can calculate real distances, areas, and even volumes. At the end you will see how many real kilometers there are in 8 cm on a $1:250{,}000$ map.

What is scale?

Conversion of a 8 cm distance on a map with a scale of 1:250,000 to its real value of 20 km through successive steps in centimeters and meters. 8 cm map 1 : 250,000 8 cm on the map = 2,000,000 real cm = 20,000 m = 20 km

The hook is already closed: 8 cm on a $1:250{,}000$ map is $20$ real km.

What if I'm asked for the scale?

If you know a measurement on the drawing and the real one, convert both to the same unit and form the ratio $\text{drawing} : \text{real}$. Then simplify so that the first number is $1$.

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A group of archaeologists has drawn an ancient vase on paper. In the drawing, the vase is $15\text{ cm}$ high. If we know that the actual vase has a height of…

A group of archaeologists has drawn an ancient vase on paper. In the drawing, the vase is $15\text{ cm}$ high. If we know that the actual vase has a height of $75\text{ cm}$, what scale have the archaeologists used?

Solve
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In a model of a famous communications tower, the height of the replica is $85$ cm. If we know that the actual height of the tower is $255$ meters, determine the…

In a model of a famous communications tower, the height of the replica is $85$ cm. If we know that the actual height of the tower is $255$ meters, determine the simplified numerical scale to which the model was built.

Solve

From the plan to reality, and back

With real distances you can also calculate times: first you get the kilometers and then you use $\text{time} = \text{distance} \div \text{speed}$.

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On a road map of Mexico, the given scale is $1:250,000$. If you use a ruler to measure the distance between two towns and measure exactly $8\text{ cm}$, how many…

On a road map of Mexico, the given scale is $1:250,000$. If you use a ruler to measure the distance between two towns and measure exactly $8\text{ cm}$, how many kilometers apart are these two towns in reality?

SCALE 1:250 000 A B Map distance: 8 cm Real distance: ? km
Solve
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On a hiking map of the Nevado de Toluca, the scale indicated is $1:25,000$. If the distance measured with a ruler between the Parque de los Venados and the Laguna del…

On a hiking map of the Nevado de Toluca, the scale indicated is $1:25,000$. If the distance measured with a ruler between the Parque de los Venados and the Laguna del Sol is $12.4$ cm on paper, how many actual kilometers will a group of hikers have to travel to go from one point to the other in a straight line?

N 12.4 cm 12.4 cm Parque de los Venados Parque de los Venados Laguna del Sol Laguna del Sol SCALE 1:25 000 1 cm on map ➔ 25 000 actual cm Actual distance: d = ? km
Solve
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On a road map of Mexico with a scale of $1:2,500,000$, the distance measured with a ruler between Mexico City and Guadalajara is $14.2\text{ cm}$. A delivery truck…

On a road map of Mexico with a scale of $1:2,500,000$, the distance measured with a ruler between Mexico City and Guadalajara is $14.2\text{ cm}$. A delivery truck leaves Mexico City at $08:00\text{ h}$ and travels toward Guadalajara at an average speed of $90\text{ km/h}$.

What time is it expected to arrive at its destination if it stops for half an hour halfway through to rest?

Scale 1:2 500 000 14.2 cm (on the map) Mexico City Guadalajara Departure: 08:00 h Arrival: ? h Rest break 30 min v = 90 km/h Actual distance = ? km
Solve

Reduction and enlargement

Not all scales shrink things. A biologist who draws an ant with a magnifying glass needs to enlarge.

In an enlargement $k:1$ the procedure is reversed: the real measurement is the drawing's measurement divided by $k$.

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A biologist photographs a small queen ant using an enlargement scale of $5:1$. If in the photograph the ant measures $45\text{ mm}$ in length, what is its actual size in…

A biologist photographs a small queen ant using an enlargement scale of $5:1$. If in the photograph the ant measures $45\text{ mm}$ in length, what is its actual size in millimeters?

Solve
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A model car collector has a scale model of $1:24$. If the length of the miniature is $18\text{ cm}$, how long will the actual car be in meters?

A model car collector has a scale model of $1:24$. If the length of the miniature is $18\text{ cm}$, how long will the actual car be in meters?

Solve
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A biologist observes an ant through a microscope. In their technical drawing, the ant has a length of $12$ cm. If the scale of the drawing is an enlargement of $25:1$,…

A biologist observes an ant through a microscope. In their technical drawing, the ant has a length of $12$ cm. If the scale of the drawing is an enlargement of $25:1$, what is the actual length of the ant expressed in millimeters?

Solve

Drawing a scale plan

To draw a room to scale, convert each real measurement to centimeters and divide by $k$.

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You want to make a drawing in your notebook of your new graphics tablet. The tablet has an actual length of $30\text{ cm}$. If you decide to use a reduction scale of…

You want to make a drawing in your notebook of your new graphics tablet. The tablet has an actual length of $30\text{ cm}$. If you decide to use a reduction scale of $1:3$, what will the length of the drawing in your notebook be?

Actual tablet L = 30 cm Scale 1:3 (÷ 3) Drawing x = ?
Solve
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On the floor plan of a house drawn to a scale of $1:100$, the main bedroom is represented as a rectangle measuring $4\text{ cm}$ long and $3\text{ cm}$ wide. Calculate…

On the floor plan of a house drawn to a scale of $1:100$, the main bedroom is represented as a rectangle measuring $4\text{ cm}$ long and $3\text{ cm}$ wide. Calculate the actual dimensions of the room expressed in meters.

PLAN 4 cm 3 cm SCALE 1:100 ACTUAL L = ? m A = ? m
Solve
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You have decided to redecorate your room and want to draw a scale plan at $1:20$ to see if a new desk fits. If your room is rectangular and measures $4.2$ meters long by…

You have decided to redecorate your room and want to draw a scale plan at $1:20$ to see if a new desk fits. If your room is rectangular and measures $4.2$ meters long by $3.4$ meters wide, what will the dimensions (length and width) of the rectangle in your drawing be, expressed in centimeters?

4.2 m 3.4 m Room Actual Scale 1:20 m → cm L = ? cm A = ? cm Plan
Solve

Graphic scale

Many maps include a bar with marked segments: this is the graphic scale. It tells you, for example, that $2\text{ cm}$ on the map are $15\text{ km}$ in real life. It works like a ruler for direct proportionality.

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You see a linear scale on a hiking map where a segment of $1\text{ cm}$ is equivalent to $500\text{ meters}$ in reality. If the route you want to do measures…

You see a linear scale on a hiking map where a segment of $1\text{ cm}$ is equivalent to $500\text{ meters}$ in reality. If the route you want to do measures $12\text{ cm}$ on the map, how many kilometers will you walk in total?

Start Finish Map: 12 cm Actual: ? km 0 500m 1km 1.5km 2km 1 cm
Solve
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A road map has a linear scale in which a segment of $2$ cm represents an actual distance of $15$ km. If the distance between two cities on that map is $9.4$ cm, what is…

A road map has a linear scale in which a segment of $2$ cm represents an actual distance of $15$ km. If the distance between two cities on that map is $9.4$ cm, what is the actual distance in kilometers between both cities?

City A City B 9.4 cm ? km SCALE 0 15 km 2 cm
Solve
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An old map has lost its numerical scale indication. However, it shows a linear scale in which a line segment measuring $3.5\text{ cm}$ on paper represents an actual…

An old map has lost its numerical scale indication. However, it shows a linear scale in which a line segment measuring $3.5\text{ cm}$ on paper represents an actual distance of $17.5\text{ kilometers}$.

  1. Determine the numerical scale of the map.

  2. If two towns are separated on the map by $12\text{ cm}$, how many hours will it take a cyclist to go from one to the other at a constant speed of $24\text{ km/h}$?

Actual Map 0 17.5 35.0 52.5 70.0 km 3.5 cm 12 cm ? km v = 24 km/h t = ? h Town A Town B
Solve

Changing scale

Sometimes you have to go from one scale to another, for example to print a smaller map. Reality does not change, so use it as a bridge.

Two maps of the same real distance: one of 12 cm at a scale of 1:50,000 and another of 4 cm at a scale of 1:150,000, linked by the same reality. 12 cm 1 : 50,000 same reality 4 cm 1 : ? 1 : 150,000 4 cm is 3 times less than 12 cm, so 1 : 50,000 × 3

The figure shows the same method with other data: $12\times 50{,}000 = 600{,}000\text{ cm}$ real, and $600{,}000 \div 4 = 150{,}000$.

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You have two different maps of the same area. On Map A, the distance between two villages is $6$ cm and the scale is $1:50,000$. On Map B, the distance between the same…

You have two different maps of the same area. On Map A, the distance between two villages is $6$ cm and the scale is $1:50,000$. On Map B, the distance between the same villages is $15$ cm. Calculate the numerical scale of Map B.

Solve
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A forest monitoring drone flies along a rectangular route over a nature park. At the control center, technicians view the route on a digital screen where the scale is…

A forest monitoring drone flies along a rectangular route over a nature park. At the control center, technicians view the route on a digital screen where the scale is $1:50,000$. On this screen, the rectangle measures $12\text{ cm}$ long and $8\text{ cm}$ wide. However, for the printed report, they must reduce the map so that the length of the route is only $4\text{ cm}$ long.

Calculate:

  1. The actual area of the nature park in square kilometers ($\text{km}^2$).

  2. The numerical scale that the map in the printed report should have.

Digital Screen Printed Report Scale 1:50 000 12 cm 8 cm Reduction Scale 1:? 4 cm ? cm Actual Area = ? km²
Solve
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A photocopy has been made of an original plan that was at a scale of $1:200$. Due to a setting error, the photocopy has come out reduced to $75\%$ of its original size.…

A photocopy has been made of an original plan that was at a scale of $1:200$. Due to a setting error, the photocopy has come out reduced to $75\%$ of its original size.

On the photocopy, the living room of the house measures $6\text{ cm}$ in length.

  1. What is the actual scale of the photocopy compared to reality?

  2. What is the actual length of the living room in meters?

REALITY L = ? m ORIGINAL PLAN L = ? cm PHOTOCOPY L = 6 cm Scale 1:200 75% reduction × 0.75 Actual Scale = ?
Solve

Scale, areas, and volumes

The scale $1:k$ multiplies lengths by $k$. Areas are multiplied by $k^2$, because an area is the product of two lengths.

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The plan of a local soccer field is drawn to a scale of $1:400$. On the plan, the area occupied by the grass is a rectangle $25$ cm long by $15$ cm wide. Calculate the…

The plan of a local soccer field is drawn to a scale of $1:400$. On the plan, the area occupied by the grass is a rectangle $25$ cm long by $15$ cm wide. Calculate the actual area of the soccer field in square meters.

Escala 1:400 25 cm 15 cm
Solve
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You are designing your own "Gaming Room" on a scale plan at $1:40$. In the drawing, the room has an area of $75\text{ cm}^2$. You have seen a professional desk that…

You are designing your own "Gaming Room" on a scale plan at $1:40$. In the drawing, the room has an area of $75\text{ cm}^2$. You have seen a professional desk that takes up an actual area of $1.28\text{ m}^2$ and a chair that takes up $0.6\text{ m}^2$.

If you decide to place the desk and two identical chairs, what actual area will remain free in the room? Express your answer in square meters ($\text{m}^2$).

PLAN Scale 1:40 75 cm² × 40² Area scale ACTUAL ROOM Total Area = ? m² Desk 1.28 m² Chair 0.6 m² Chair 0.6 m² FREE AREA ? m²
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An architect has built a scale model of a new auditorium at a scale of $1:250$. The total volume of the model is $0.64\text{ dm}^3$. Given that the density of the actual…

An architect has built a scale model of a new auditorium at a scale of $1:250$. The total volume of the model is $0.64\text{ dm}^3$.

Given that the density of the actual materials is different, but the volume remains proportional to the cube of the scale factor, calculate the actual volume of the auditorium in cubic meters ($\text{m}^3$).

(Note: Remember that if the length scale factor is $k$, the volume scale factor is $k^3$).

Scale model V = 0.64 dm³ Actual Auditorium V = ? m³ Scale k = 250 Volume × 250³
Solve

Summary

See all the exercises in this section