A kiosk had lemon drinks and orange drinks in the ratio 3 : 5 at first. The kiosk sold 15 lemon drinks and received 40 more orange drinks. After this, the ratio of the number of lemon drinks to the number of orange drinks became 1 : 2. How many drinks were there altogether at first?
- 210
- 350
- 560
- 585
Need a hint?
Write the first amounts in units of the ratio, then write the amounts after the change and set up the new ratio 1 : 2 as an equation.
Worked answer
- At first, lemon : orange = 3 : 5, so each unit is 1 part of the ratio.
- Let each unit be u drinks. Lemon at first is 3u and orange at first is 5u.
- After the change, lemon = 3u − 15 and orange = 5u + 40.
- The new ratio is 1 : 2, so orange = 2 × lemon: 5u + 40 = 2(3u − 15) = 6u − 30.
- So u = 70. Lemon at first = 210 and orange at first = 350.
- Total at first = 210 + 350 = 560.
Answer: 560 drinks
The mistake this question tests
Habit
Left out the units
Pupils often take the orange drinks alone as the total, or add the changes to the first amounts without solving for the unit.
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See the answer →Practise PSLE ratio until the mistakes stop.
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