Ratio Problems

Question 12 marks

The ratios red : blue and blue : green are 2:3 and 3:4.

Write red : blue : green as a:3:c.

(a)

Value of a.

1 mark

(b)

Value of c.

1 mark

Hint

The blue parts already agree.

Worked solution

The ratios red : blue and blue : green are 2:3 and 3:4.

Write red : blue : green as a:3:c.

Part (a)

Value of a.

  1. Both ratios use 3 blue parts, so red : blue : green is 2:3:4.

Part (b)

Value of c.

  1. The simplified ratio gives c=4.

Question 23 marks

The ratios A:B=3:4 and B:C=8:5.

Write A:B:C in its simplest form as a:b:c.

(a)

Value of a.

1 mark

(b)

Value of b.

1 mark

(c)

Value of c.

1 mark

Hint

Match the B parts.

Worked solution

The ratios A:B=3:4 and B:C=8:5.

Write A:B:C in its simplest form as a:b:c.

Part (a)

Value of a.

  1. 3:4=6:8.
  2. The combined ratio is 6:8:5, with no common factor.

Part (b)

Value of b.

  1. The simplified ratio gives b=8.

Part (c)

Value of c.

  1. The simplified ratio gives c=5.

Question 33 marks

The ratios P:Q=2:3 and Q:R=4:5.

Write P:Q:R in its simplest form as a:b:c.

(a)

Value of a.

1 mark

(b)

Value of b.

1 mark

(c)

Value of c.

1 mark

Hint

Use a common multiple for the Q parts.

Worked solution

The ratios P:Q=2:3 and Q:R=4:5.

Write P:Q:R in its simplest form as a:b:c.

Part (a)

Value of a.

  1. 2:3=8:12 and 4:5=12:15.
  2. The combined ratio is 8:12:15.

Part (b)

Value of b.

  1. The simplified ratio gives b=12.

Part (c)

Value of c.

  1. The simplified ratio gives c=15.

Question 42 marks

The ratios A:B=3:5 and B:C=2:7.

Write A:C in its simplest form as a:c.

(a)

Value of a.

1 mark

(b)

Value of c.

1 mark

Hint

Match B, then select only A and C.

Worked solution

The ratios A:B=3:5 and B:C=2:7.

Write A:C in its simplest form as a:c.

Part (a)

Value of a.

  1. A:B=6:10 and B:C=10:35.
  2. So A:C=6:35.

Part (b)

Value of c.

  1. The simplified ratio gives c=35.

Question 52 marks

The ratios blue : red =3:4 and blue : green =6:5.

Write red : green in its simplest form as a:b.

(a)

Value of a.

1 mark

(b)

Value of b.

1 mark

Hint

Notice that blue is first in both given ratios.

Worked solution

The ratios blue : red =3:4 and blue : green =6:5.

Write red : green in its simplest form as a:b.

Part (a)

Value of a.

  1. Blue : red =6:8.
  2. With 6 blue parts there are 8 red and 5 green parts, giving 8:5.

Part (b)

Value of b.

  1. The simplified ratio gives b=5.

Question 63 marks

There are two-thirds as many red beads as blue beads. The ratio blue : yellow is 4:5.

Write red : blue : yellow in its simplest form as a:b:c.

(a)

Value of a.

1 mark

(b)

Value of b.

1 mark

(c)

Value of c.

1 mark

Hint

For every 3 blue beads, how many red beads are there?

Worked solution

There are two-thirds as many red beads as blue beads. The ratio blue : yellow is 4:5.

Write red : blue : yellow in its simplest form as a:b:c.

Part (a)

Value of a.

  1. Red : blue =2:3=8:12.
  2. Blue : yellow =4:5=12:15.
  3. The ratio is 8:12:15.

Part (b)

Value of b.

  1. The simplified ratio gives b=12.

Part (c)

Value of c.

  1. The simplified ratio gives c=15.

Question 73 marks

In a mixture, the mass ratio oats : raisins is 3:4, and raisins : seeds is 6:5.

Write oats : raisins : seeds in its simplest form as a:b:c.

(a)

Value of a.

1 mark

(b)

Value of b.

1 mark

(c)

Value of c.

1 mark

Hint

Use the same number of raisin parts.

Worked solution

In a mixture, the mass ratio oats : raisins is 3:4, and raisins : seeds is 6:5.

Write oats : raisins : seeds in its simplest form as a:b:c.

Part (a)

Value of a.

  1. Oats : raisins =9:12. Raisins : seeds =12:10.
  2. The combined ratio is 9:12:10.

Part (b)

Value of b.

  1. The simplified ratio gives b=12.

Part (c)

Value of c.

  1. The simplified ratio gives c=10.

Question 82 marks

The ratios A:B=3:5, B:C=10:x and A:C=6:7.

Work out x.

Hint

Use 6 A parts to link the statements.

Worked solution

The ratios A:B=3:5, B:C=10:x and A:C=6:7.

Work out x.

  1. A:B=6:10.
  2. When A has 6 parts, C has 7, so B:C=10:7 and x=7.

Question 93 marks

A stall receives £3 from each of 24 morning customers, £4 from each of 18 afternoon customers, and £36 in donations.

Write morning income : afternoon income : donations in its simplest form as a:b:c.

(a)

Value of a.

1 mark

(b)

Value of b.

1 mark

(c)

Value of c.

1 mark

Hint

Calculate each income before forming the ratio.

Worked solution

A stall receives £3 from each of 24 morning customers, £4 from each of 18 afternoon customers, and £36 in donations.

Write morning income : afternoon income : donations in its simplest form as a:b:c.

Part (a)

Value of a.

  1. Morning: 24\times3=72 pounds. Afternoon: 18\times4=72 pounds.
  2. 72:72:36=2:2:1.

Part (b)

Value of b.

  1. The simplified ratio gives b=2.

Part (c)

Value of c.

  1. The simplified ratio gives c=1.

Question 103 marks

A box contains only red, blue and green counters. Red : blue =3:2 and blue : green =4:5.

What fraction of all the counters are blue?

Hint

Combine the ratios before finding the whole.

Worked solution

A box contains only red, blue and green counters. Red : blue =3:2 and blue : green =4:5.

What fraction of all the counters are blue?

  1. Red : blue : green =6:4:5.
  2. Total parts: 6+4+5=15. Blue fraction: \frac4{15}.

Question 113 marks

A jar contains only red, orange and yellow sweets.

For every 2 red sweets there are 3 orange sweets. For every 6 orange sweets there are 5 yellow sweets.

There are 180 sweets in the jar. Work out the number of orange sweets.

Hint

Make the number of orange parts the same in both ratios, then use the total.

Worked solution

A jar contains only red, orange and yellow sweets.

For every 2 red sweets there are 3 orange sweets. For every 6 orange sweets there are 5 yellow sweets.

There are 180 sweets in the jar. Work out the number of orange sweets.

  1. Red : orange =2:3=4:6, and orange : yellow =6:5.
  2. So red : orange : yellow =4:6:5, which is 4+6+5=15 parts.
  3. One part: 180\div15=12 sweets.
  4. Orange: 6\times12=72 sweets.

Question 123 marks

There are 45 red beads. Red : blue =3:4 and blue : green =5:6.

Work out the number of green beads.

Hint

You can find blue first, then green.

Worked solution

There are 45 red beads. Red : blue =3:4 and blue : green =5:6.

Work out the number of green beads.

  1. Blue: 45\div3\times4=60.
  2. Green: 60\div5\times6=72.

Question 133 marks

Drink A has concentrate : water =2:7. Drink B has concentrate : water =3:11.

Each drink is made using 77 litres of water. How many more litres of concentrate are used for A than for B?

Hint

Compare the concentrate amounts for the same water amount.

Worked solution

Drink A has concentrate : water =2:7. Drink B has concentrate : water =3:11.

Each drink is made using 77 litres of water. How many more litres of concentrate are used for A than for B?

  1. A concentrate: 77\div7\times2=22 litres.
  2. B concentrate: 77\div11\times3=21 litres.
  3. Difference: 22-21=1 litre.

Question 144 marks

Bag A has 40 counters with red : blue =2:3. Bag B has 30 counters with red : blue =1:4.

All counters are put together. Write red : blue in its simplest form as a:b.

(a)

Value of a.

2 marks

(b)

Value of b.

2 marks

Hint

Find actual colour counts before combining the bags.

Worked solution

Bag A has 40 counters with red : blue =2:3. Bag B has 30 counters with red : blue =1:4.

All counters are put together. Write red : blue in its simplest form as a:b.

Part (a)

Value of a.

  1. Bag A: 40\div5=8, so 16 red and 24 blue. Bag B: 30\div5=6, so 6 red and 24 blue.
  2. Altogether: 22 red and 48 blue, so 22:48=11:24.

Part (b)

Value of b.

  1. The simplified ratio gives b=24.

Question 153 marks

A collection has 100 beads in the ratio red : blue : green =2:3:5. Ten blue beads are removed.

Write the new red : blue : green ratio in its simplest form as a:b:c.

(a)

Value of a.

1 mark

(b)

Value of b.

1 mark

(c)

Value of c.

1 mark

Hint

Change the number of blue beads, not every ratio term.

Worked solution

A collection has 100 beads in the ratio red : blue : green =2:3:5. Ten blue beads are removed.

Write the new red : blue : green ratio in its simplest form as a:b:c.

Part (a)

Value of a.

  1. Original counts:20 red,30 blue,50 green.
  2. New counts:20 red,20 blue,50 green.
  3. 20:20:50=2:2:5.

Part (b)

Value of b.

  1. The simplified ratio gives b=2.

Part (c)

Value of c.

  1. The simplified ratio gives c=5.

Question 16Challenge4 marks

A bag contains only red, blue and green counters.

Red : blue =4:3 and blue : green =2:5.

There are at least 40 more green counters than red counters.

Work out the least possible total number of counters in the bag.

Hint

Write red : blue : green as one ratio. How many more parts does green have than red?

Worked solution

A bag contains only red, blue and green counters.

Red : blue =4:3 and blue : green =2:5.

There are at least 40 more green counters than red counters.

Work out the least possible total number of counters in the bag.

  1. Red : blue =4:3=8:6 and blue : green =2:5=6:15, so red : blue : green =8:6:15.
  2. Green has 15-8=7 more parts than red.
  3. 5 parts each: 7\times5=35 more green counters, which is fewer than 40. 6 parts each: 7\times6=42, which is at least 40.
  4. So the least is 6 counters per part. Total parts: 8+6+15=29.
  5. Least possible total: 29\times6=174 counters.

Question 17Challenge4 marks

A bag initially has red : blue counters =3:5. Twelve red counters are added, with no blue counters added. The new ratio is 3:4.

Work out the original number of red counters.

Hint

Compare the ratios using the unchanged number of blue counters.

Worked solution

A bag initially has red : blue counters =3:5. Twelve red counters are added, with no blue counters added. The new ratio is 3:4.

Work out the original number of red counters.

  1. Original red : blue =12:20. New red : blue =15:20.
  2. The extra 3 parts are 12 counters, so one part is 4 counters.
  3. Original red: 12\times4=48.

Question 18Challenge4 marks

A box contains 310 counters, all red, blue or green. Red : blue =3:5 and blue : green =2:3. One-third of the green counters are removed.

What fraction of the remaining counters are blue?

Hint

Find the original counts and update the total after removal.

Worked solution

A box contains 310 counters, all red, blue or green. Red : blue =3:5 and blue : green =2:3. One-third of the green counters are removed.

What fraction of the remaining counters are blue?

  1. Combined ratio: 6:10:15, totalling 31 parts.
  2. There are 60 red,100 blue and 150 green counters.
  3. 50 green counters leave, so 310-50=260 remain.
  4. Blue fraction: 100/260=5/13.

Question 19Challenge4 marks

The ratios A:B=4:7 and B:C=3:2. The value of C is 10 greater than the value of A.

Work out B.

Hint

Use the difference between A and C in the combined ratio.

Worked solution

The ratios A:B=4:7 and B:C=3:2. The value of C is 10 greater than the value of A.

Work out B.

  1. A:B:C=12:21:14.
  2. The difference is 2 parts, so one part is 10\div2=5.
  3. B=21\times5=105.

Question 20Challenge5 marks

Drink A has concentrate : water =1:3. Drink B has concentrate : water =2:3.

600 ml of A is mixed with 500 ml of B. Water is then added until concentrate : water =1:3.

Work out how much water is added, in millilitres.

Hint

Work with actual concentrate and water volumes.

Worked solution

Drink A has concentrate : water =1:3. Drink B has concentrate : water =2:3.

600 ml of A is mixed with 500 ml of B. Water is then added until concentrate : water =1:3.

Work out how much water is added, in millilitres.

  1. A contains 150 ml concentrate and 450 ml water.
  2. B contains 200 ml concentrate and 300 ml water.
  3. Combined: 350 ml of concentrate and 750 ml of water.
  4. For 1:3, water must be 350\times3=1050 ml.
  5. Add 1050-750=300 ml of water.