A pet shop has 150 guppies and 90 betta fish.
- What is the ratio of the number of guppies to the number of betta fish in its simplest form?
- Later, the shop receives more betta fish so that the ratio of the number of guppies to the number of betta fish becomes 5 : 6. The number of guppies stays at 150. How many more betta fish does the shop receive?
Need a hint?
In part (b), find the value of one unit from the guppies first, then work out the new number of betta fish.
Worked answer
- (a) Divide both 150 and 90 by their highest common factor, 30.
- (a) 150 : 90 = 5 : 3.
- (b) In the new ratio, guppies are 5 units and this equals 150 fish.
- (b) 1 unit = 150 ÷ 5 = 30 fish.
- (b) Betta fish are 6 units, so 6 × 30 = 180 betta fish.
- (b) More betta fish received = 180 − 90 = 90.
Answer: 90 betta fish
The mistake this question tests
Habit
Simplest form in final fraction answers
Pupils often stop at 180, which is the new total of betta fish, and forget to subtract the 90 the shop already had.
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