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ESO Y1 · Mathematics
Arithmetic · Proportion

Ratio and proportion

In a fruit bowl there are 3 apples and 2 pears. On a plan, 1 cm represents 300 real metres. In a recipe, for every 2 cups of flour you use 1 of water. All three sentences compare two quantities by dividing: that is a ratio.

Ratio between two quantities

In a 1st ESO class there are 12 students who play basketball and 18 who play football. The basketball/football ratio is $\frac{12}{18} = \frac{2}{3}$: for every 2 who play basketball, there are 3 who play football.

Diagram illustrating the ratio of 12 basketballs to 18 footballs grouped in 2s and 3s to show the simplified ratio 2 to 3. 12 basketball18 football ratio 12 : 18 = 2 : 3
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In a Year 7 class, there are $12$ pupils who play basketball and $18$ pupils who play football. Write the ratio of the number of basketball players to football players.…

In a Year 7 class, there are $12$ pupils who play basketball and $18$ pupils who play football. Write the ratio of the number of basketball players to football players. Explain in your own words what the result means after simplifying the fraction.

Solve
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In an adventure video game, your character has obtained $24$ health potions after opening $6$ magic chests. Calculate the ratio of the number of potions to the number of…

In an adventure video game, your character has obtained $24$ health potions after opening $6$ magic chests. Calculate the ratio of the number of potions to the number of chests. On average, how many health potions are there in each chest?

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Simplifying a ratio

A ratio is simplified in the same way as a fraction: by dividing both terms by the same number until you can go no further.

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A radio-controlled car travels a distance of $45$ metres in $15$ seconds. Calculate the ratio of distance to time. What physical quantity does this result represent?

A radio-controlled car travels a distance of $45$ metres in $15$ seconds. Calculate the ratio of distance to time. What physical quantity does this result represent?

0 m 45 m d = 45 m t = 15 s v = ?
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In a basketball training session, Lucía scored $18$ three-pointers out of $30$ shots taken, while her teammate Marcos scored $14$ three-pointers out of $20$ shots. a)…

In a basketball training session, Lucía scored $18$ three-pointers out of $30$ shots taken, while her teammate Marcos scored $14$ three-pointers out of $20$ shots.

  1. a) Express the success ratio of each player as a decimal number.
  2. b) Which of the two has a better success ratio? Justify your answer by comparing both values.
0 5 10 15 20 25 30 Shots Lucía 18/30 Marcos 14/20
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Maps, plans and scales

Representation of a scale relating the distance measured on a plan to the equivalent distance in reality. 1 cm plan 1 : 300 000 1 cm on the plan = 300 000 real cm = 3 000 m = 3 km
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In your Year 7 class there are $32$ pupils in total. It is known that for every $3$ pupils who prefer PE classes, there are $5$ pupils who prefer Art. a) Write the ratio…

In your Year 7 class there are $32$ pupils in total. It is known that for every $3$ pupils who prefer PE classes, there are $5$ pupils who prefer Art.

  1. a) Write the ratio of those who prefer PE to those who prefer Art.
  2. b) If these are the only two options and everyone has chosen one, how many pupils prefer each subject? (Hint: notice that the sum of the terms in the simplified ratio is $3 + 5 = 8$).
PE Art 3 parts 5 parts Total = 32 pupils (3 + 5 = 8 parts)
Solve
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In competitive video gaming, server performance is measured by the ratio of connected players to bandwidth consumed (in Mbps). The "BattleArena" server has $120$ players…

In competitive video gaming, server performance is measured by the ratio of connected players to bandwidth consumed (in Mbps). The "BattleArena" server has $120$ players and consumes $450$ Mbps. On the other hand, the "GalaxyQuest" server has $85$ players and consumes $320$ Mbps. Calculate the consumption ratio per player for both servers and determine which of the two is more efficient (the one consuming fewer Mbps per player). Express the ratios as decimals.

BattleArena 450 Mbps 120 jug. ? Mbps / player GalaxyQuest 320 Mbps 85 jug. ? Mbps / player VS
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Proportions: the equality of ratios

Diagram of the cross-product rule in a proportion relating the extremes 2 and x to the means 5 and 10. 25=10x extremes: 2 · x means: 5 · 10 = 50

If you know three terms of the proportion, you can find the fourth by rearranging:

$$\frac{2}{5} = \frac{10}{x} \ \Rightarrow\ 2x = 50 \ \Rightarrow\ x = 25$$
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Look at these two mixtures of water and strawberry syrup. Mixture $A$ has $2$ glasses of syrup for every $5$ glasses of water. Mixture $B$ has $4$ glasses of syrup for…

Look at these two mixtures of water and strawberry syrup. Mixture $A$ has $2$ glasses of syrup for every $5$ glasses of water. Mixture $B$ has $4$ glasses of syrup for every $10$ glasses of water.

  • Write the ratio for each mixture.

  • Are these mixtures proportional? That is, will they taste the same?

Glass of syrup Glass of water Mixture A 2 de sirope por 5 de agua Mixture B 4 de sirope por 10 de agua
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In a strategy video game, to craft a "Super Speed" potion, the alchemist uses $150\text{ mg}$ of stardust for every $250\text{ ml}$ of magic water. a) Express the ratio…

In a strategy video game, to craft a "Super Speed" potion, the alchemist uses $150\text{ mg}$ of stardust for every $250\text{ ml}$ of magic water.

  1. a) Express the ratio of stardust to magic water. Simplify the result and interpret what this value means.
  2. b) Calculate the inverse ratio (magic water to stardust) and explain what information it gives us.
Ratio = 150 mg Stardust 250 ml Magic water
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Summary

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