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Secondary 2 · Mathematics
Arithmetic · Proportionality

Proportional Distributions

Before you start, make sure you know: Direct proportionality (Secondary Year 1)
Before you start, make sure you know: Least common multiple (Secondary Year 1)

Ximena, Diego, and Valeria win a video game tournament and split $\$1{,}900$. In the final, Ximena scored 150 points, Diego 120, and Valeria 110. Is it fair to split it equally? It seems fairer for the person who earned more points to get more money. That is a proportional distribution.

Directly proportional distribution

An amount is split into parts that are proportional to some numbers: whoever has more gets more.

Change the total or the parts and watch how the bar is split:

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Three friends, Alba, Beto and Caio, collaborated at a charity market selling crafts. They decide to share the $\$300…

Three friends, Alba, Beto and Caio, collaborated at a charity market selling crafts. They decide to share the $\$300$ profit directly proportional to the number of hours each worked: Alba worked $2$ hours, Beto $3$ hours and Caio $5$ hours. Calculate how much money each receives.

Total Profit = $300 ? $ ? $ ? $ Alba 2 h Beto 3 h Caio 5 h Total Time = 10 h
Solve
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Three friends decide to rent a private server to play an online video game during the holidays. The total cost of the rental is $\$153…

Three friends decide to rent a private server to play an online video game during the holidays. The total cost of the rental is $\$153$. They have agreed to share the payment directly proportional to the time each was connected: Álex was on for $12$ hours, Bea for $18$ hours and Cristian for $21$ hours. How much should each contribute to pay the bill?

$153 Álex Bea Cristian 12 h 18 h 21 h Total = 51 h
Solve
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A carpenter has a wooden strip of $240\text{ cm}$ and needs to cut it into three pieces whose lengths are proportional to the numbers $1$, $2$ and $3$. We call $k$ the…

A carpenter has a wooden strip of $240\text{ cm}$ and needs to cut it into three pieces whose lengths are proportional to the numbers $1$, $2$ and $3$. We call $k$ the length of the shortest piece, so that the other two measure $2k$ and $3k$. What will be the length of each piece?

240 cm strip divided into three pieces of lengths k, 2k and 3k240 cmk2k3k
Solve

Inversely proportional distribution

Now whoever has more of something receives less. For example, a municipality splits a fund among schools inversely proportionally to the tons of waste they did not recycle: the one that pollutes the least gets the most.

The trick: split directly proportionally to the reciprocals $\frac{1}{a}, \frac{1}{b}, \frac{1}{c}$.

Why does it work? A small number (few absences) should give a large share. Its reciprocal, $\frac{1}{a}$, is large when $a$ is small, so the reciprocal measures the merit.

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In a video game competition, $100$ bonus points are shared between two players inversely proportional to the number of mistakes they made. If the first player made $2$…

In a video game competition, $100$ bonus points are shared between two players inversely proportional to the number of mistakes they made. If the first player made $2$ mistakes and the second made $4$ mistakes, how many points does each receive?

Solve
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A box containing $120$ tickets for a music festival is to be shared among three local secondary schools. The distribution will be made inversely proportional to the…

A box containing $120$ tickets for a music festival is to be shared among three local secondary schools. The distribution will be made inversely proportional to the number of students who arrived late on the last cultural day. School "A" had $10$ late arrivals, School "B" had $15$ late arrivals and School "C" had $30$ late arrivals. How many tickets will each school receive?

Solve
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In a recycling competition, a municipality distributes a fund of $52\,000$ pesos among three schools in inverse proportion to the number of metric tons of non-recycled…

In a recycling competition, a municipality distributes a fund of $52\,000$ pesos among three schools in inverse proportion to the number of metric tons of non-recycled waste they generated. School $1$ generated $\frac{1}{2}$ metric ton, School $2$ generated $\frac{1}{3}$ of a metric ton, and School $3$ generated $\frac{1}{4}$ of a metric ton. What cash prize does each school receive?

1 t Waste Prize Fund: $52 000 School ₁ 1/2 t 2k School ₂ 1/3 t 3k School ₃ 1/4 t 4k Inversely Proportional 2k + 3k + 4k = 9k = $52 000
Solve

When a piece of data is missing

Sometimes you aren't given all the numbers, but you do get a clue: what one person received. With it you find the constant $k$ (the value of one part) and fill in everything else.

If the data come as a relationship ("triple," "half," "3 nights fewer than…"), first write down each person's number. For example, if P has $x$, Q has $3x$, and R has $\frac{3x}{2}$, the parts are proportional to $1$, $3$, and $1.5$ (or $2, 6$, and $3$).

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Three families have rented a country house for the Easter holidays. The total cost of the rent is $30\,000$ pesos. They decide to share the expense in direct proportion…

Three families have rented a country house for the Easter holidays. The total cost of the rent is $30\,000$ pesos. They decide to share the expense in direct proportion to the number of nights that each family stayed in the house. The Sánchez family stayed $5$ nights, the Pérez family stayed twice as many nights as the García family, and the García family stayed $3$ nights fewer than the Sánchez family. How much must each family pay?

Solve
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A donation of $110\,000$ pesos is shared among three charities in direct proportion to the places they offer. Charity $P$ has $x$ places, charity $Q$ has three times as…

A donation of $110\,000$ pesos is shared among three charities in direct proportion to the places they offer. Charity $P$ has $x$ places, charity $Q$ has three times as many places as $P$, and charity $R$ has half as many places as $Q$. Knowing that charity $Q$ received $60\,000$ pesos, how much money does each of the other two charities receive?

Solve
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A rectangular plot of $1\,200$ $m^2$ is divided into three school vegetable gardens for 9th grade classes. The area is divided in direct proportion to the number of…

A rectangular plot of $1\,200$ $m^2$ is divided into three school vegetable gardens for 9th grade classes. The area is divided in direct proportion to the number of students in each class. Class $A$ has $24$ students, class $B$ has $28$ students, and class $C$ has a number of students such that it received $450$ $m^2$ of garden.

  1. How many students does class $C$ have?

  2. What area corresponds to classes $A$ and $B$?

Class A 24 students ? m² Class B 28 students ? m² Class C ? students 450 m² Total Area = 1200 m²
Solve

Distributions with an extra step

Many problems don't end with the distribution: first you have to subtract an expense, or afterward you have to add a fixed amount to one of the shares.

Diagram showing how to deduct 10% from a 2,000-peso prize before splitting the net amount of 1,800 pesos. 2,000 pesos prize × 0.90 net after 10% split to each one 2,000 × 0.90 = 1,800 net amount to split
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Three friends from an e-sports club have won a regional tournament and are going to share out a $1\,900$ pesos prize. The distribution must be directly proportional to…

Three friends from an e-sports club have won a regional tournament and are going to share out a $1\,900$ pesos prize. The distribution must be directly proportional to the points scored in the grand final. The first player got $150$ points, the second $120$ points, and the third $110$ points. However, before payout, the club deducts $5\%$ of the total prize for administration fees. What net amount will each of the three players receive after applying the discount and making the proportional distribution?

Gross Prize $1900 −5% fees Net Prize 150 + 120 + 110 = 380 pts 150 pts 120 pts 110 pts J₁ ? $ J₂ ? $ J₃ ? $
Solve
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A grandfather wants to share a collection of $168$ antique coins among his three grandchildren in inverse proportion to their ages, which are $12$, $15$ and $20$ years…

A grandfather wants to share a collection of $168$ antique coins among his three grandchildren in inverse proportion to their ages, which are $12$, $15$ and $20$ years old. The youngest grandchild is so excited that the grandfather decides to give him, in addition, $10$ more coins taken from his own personal reserve. How many coins will each grandchild end up with?

Solve

Back to the beginning: splitting $\$1{,}900$ equally doesn't reward effort. With $k = 5$ pesos per point, Ximena gets $\$750$, Diego $\$600$, and Valeria $\$550$.

Summary

See all the exercises in this section