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Secondary 3 · Mathematics
Proportionality · Proportionality

Proportional Distributions

Before you start, make sure you know: Least common multiple (Secondary Year 2 (first cycle))
Before you start, make sure you know: Operations with rational numbers (Secondary Year 2 (first cycle))

Yaritza, Wilkin, and Starling win 300 pesos in a video game tournament. Yaritza played 2 games, Wilkin 3, and Starling 5. Is it fair to give 100 pesos to each one? It seems fairer for whoever played more to get more. 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, Alex, Bea and Cris, took part in a team video game tournament and won a chest with $240$ virtual gold coins. They have decided to share the loot in direct…

Three friends, Alex, Bea and Cris, took part in a team video game tournament and won a chest with $240$ virtual gold coins. They have decided to share the loot in direct proportion to the number of levels each one cleared: Alex cleared $2$ levels, Bea $3$ levels and Cris $5$ levels. How many coins does each person get?

240 coins Alex 2 levels Bea 3 levels Cris 5 levels Total: 2 + 3 + 5 = 10 parts
Solve
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A local municipality wants to reward recycling and shares $180\,000$ pesos among three schools in direct proportion to the kilograms of paper recycled. The "El Olivo"…

A local municipality wants to reward recycling and shares $180\,000$ pesos among three schools in direct proportion to the kilograms of paper recycled. The "El Olivo" school recycled $600$ kg, the "La Caoba" school $900$ kg, and the "El Pino" school $1500$ kg. Determine the amount of money each school receives.

Solve
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Three friends decide to enter a team eSports tournament. After winning first prize, the organizers give them a chest containing $2700$ virtual coins. To be fair, they…

Three friends decide to enter a team eSports tournament. After winning first prize, the organizers give them a chest containing $2700$ virtual coins. To be fair, they decide to share the coins directly proportional to the experience points (XP) each contributed in the final game: Álex contributed $12$ points, Bea $15$ points and Cristian $18$ points. How many coins does each person get?

0 5 10 15 20 XP 12 Álex 15 Bea 18 Cristian x y z C 2700 coins
Solve

Inversely proportional distribution

Now whoever has more gets less. For example, bonus points in a robotics contest are split inversely proportionally to the time each robot took: the fastest one (least time) gets the most.

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

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In a robotics contest, $140$ extra points are shared out inversely proportionally to the number of mistakes made on the course. If team "Alfa" made $1$ mistake, team…

In a robotics contest, $140$ extra points are shared out inversely proportionally to the number of mistakes made on the course. If team "Alfa" made $1$ mistake, team "Beta" made $2$ mistakes and team "Gamma" made $4$ mistakes, how many points will each team receive?

Diagram of the sharing of 140 extra points among three teams according to their mistakes: Alfa 1 mistake, Beta 2 mistakes and Gamma 4 mistakes140 extra pointsAlfaBetaGamma1 mistake2 mistakes4 mistakesEach ✕ is a mistake made on the course
Solve
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Three friends hire a car for a trip and must pay a deposit of $180$ pesos. They decide that the return of the deposit (if there is no damage) will be shared in inverse…

Three friends hire a car for a trip and must pay a deposit of $180$ pesos. They decide that the return of the deposit (if there is no damage) will be shared in inverse proportion to the number of times each one had to be warned by the driver for not wearing a seatbelt. If Dani had $2$ warnings, Elena $3$ warnings and Fede $6$ warnings, what portion of the $180$ pesos will each person get back?

INVERSE SHARING CAR DEPOSIT RD$180 DANI 2 warnings ∝ 1/2 ELENA 3 warnings ∝ 1/3 FEDE 6 warnings ∝ 1/6
Solve
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Three siblings have to share household chores. Their mother has decided that the number of hours each one will spend cleaning the garden will be inversely proportional…

Three siblings have to share household chores. Their mother has decided that the number of hours each one will spend cleaning the garden will be inversely proportional to their average marks for the school year: Arnau has $9$, Amina $8$ and Jorge $6$. If they have to cover $74$ hours of work in total between the three of them, how many hours does each one get?

Solve

Discounts, donations, and rounding

Sometimes the problem adds a step: a discount on the total, a donation of one share, or a result that doesn't come out as a whole number. The key is the order.

  • Discount or surcharge on the total: first find the new total and then split.

  • Donation of one share (for example, 25% of what one person receives): first split, and then apply the percent to that share.

  • Non-whole result (comic books, people…): round to the nearest unit and check whether the sum still equals the total. If it doesn't, the distribution is not exact and you have to decide who gets the unit that is left over or missing.

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To encourage reading, a youth library is distributing a set of $155$ comics among the three users who have read the most books in the last term. The distribution will be…

To encourage reading, a youth library is distributing a set of $155$ comics among the three users who have read the most books in the last term. The distribution will be directly proportional to the number of books read. If the users read $12$, $18$ and $32$ books respectively, how many comics will each one receive? (Note: If the result is not a whole number, round to the nearest unit and state whether the division is exact).

155 COMICS Total books = 12 + 18 + 32 = 62 books 12 User 1 x₁ comics books 18 User 2 x₂ comics books 32 User 3 x₃ comics
Solve
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A group of three farmers decides to hire machinery for $\text{RD\$}\ 570$. The cost will be shared directly proportional to the area of their plots, which measure $3…

A group of three farmers decides to hire machinery for $\text{RD\$}\ 570$. The cost will be shared directly proportional to the area of their plots, which measure $3$, $5$ and $7$ hectares respectively. However, the owner of the machinery gives them a $10 \%$ discount on the total because it is off-season. How much will each farmer have to pay after applying the discount?

Cost: RD$570 (−10%) 3 ha 5 ha 7 ha Total area = 15 ha
Solve
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A grandfather wishes to divide $\text{RD\$}\ 2\,664\,000$ among his three grandchildren aged $15, 20$ and $30…

A grandfather wishes to divide $\text{RD\$}\ 2\,664\,000$ among his three grandchildren aged $15, 20$ and $30$ years so that the division is inversely proportional to their ages. Before the division is made, the middle grandchild decides to donate $25\%$ of their share to an NGO. What net amount will the $20$-year-old grandchild end up receiving?

Solve

Distributions with two criteria

Sometimes an amount is split according to two things at once: for example, the money invested and the time it was invested. You multiply each person's numbers and split proportionally to those products.

Three rectangles whose areas represent the product of money times time for each partner in order to carry out the compound distribution. 2,000 × 6 3,000 × 4 5,000 × 2 "area" of each partner = money × time → split according to those areas
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Three partners in an eco-friendly courier startup initially invested different amounts: $\text{RD\$}\ 4000$, $\text{RD\$}\ 7000$ and $\text{RD\$}\ 9000…

Three partners in an eco-friendly courier startup initially invested different amounts: $\text{RD\$}\ 4000$, $\text{RD\$}\ 7000$ and $\text{RD\$}\ 9000$. At the end of the year, they made a net profit of $\text{RD\$}\ 12000$. How should the profits be divided directly proportional to their initial investment?

Total Investment = RD$20 000 (20 parts) Total Profit = RD$12 000 RD$4 000 RD$7 000 RD$9 000 4 parts 7 parts 9 parts B₁ = ? B₂ = ? B₃ = ?
Solve

Challenges: comparing methods

Now you have the tools. Before calculating, ask yourself:

  • Is the distribution direct or inverse?

  • Is there a step before (discount) or after (donation) the distribution?

  • Who should get the most? If your result doesn't satisfy that, check your method.

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A relay competition awards $\text{RD\$}\ 54\,000…

A relay competition awards $\text{RD\$}\ 54\,000$ among the three teams that crossed the finish line first. The prize is inversely proportional to the total time taken. Team "Rayo" took $10$ minutes, team "Gacela" took $12$ minutes and team "Flecha" took $15$ minutes. What amount of money does each team receive? Explain why the team that took the least time receives the largest amount.

Solve
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An Escape Room company offers a monthly voucher of $\text{RD\$}\ 450…

An Escape Room company offers a monthly voucher of $\text{RD\$}\ 450$ to be shared among the three teams that manage to escape their hardest room in under an hour. The prize is divided inversely proportional to the time taken. Team "Alpha" escaped in $40$ minutes, team "Beta" in $45$ minutes and team "Gamma" in $50$ minutes. Calculate the share of the prize that each team receives.

Alpha 40 min k/40
Solve
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Three municipalities decide to subsidize a reforestation project with a total of $\text{RD\$}\ 7\,200\,000…

Three municipalities decide to subsidize a reforestation project with a total of $\text{RD\$}\ 7\,200\,000$. The contribution of each municipality will be inversely proportional to the number of hectares of forest burned in its municipal area the previous year. Municipality A had $200$ ha burned, Municipality B had $500$ ha, and Municipality C had $800$ ha. If the municipality with the most fires appeals the decision and it is decided that the distribution should be directly proportional to those hectares to help those most affected, what would be the difference in money for Municipality B between the first method and the second?

Solve

Back to the beginning: Yaritza, Wilkin, and Starling should not get 100 pesos each, but 60, 90, and 150 pesos, in proportion to the games they played.

Summary

See all the exercises in this section