Nurul bought some ferns and cacti for the school garden. 35 of the plants were ferns and the rest were cacti. Each cactus cost $2 less than each fern. She spent a total of $372 on both ferns and cacti. The total cost of the ferns was $132 more than the total cost of the cacti.
- What was the total cost of the cacti?
- How much did each fern cost?
Need a hint?
Find the total cost of each kind of plant first. Then think of 1 unit as the same number of ferns and cacti, and see how the $2 difference in price shows up in the cost of 1 unit.
Worked answer
- (a) Take away the extra cost of the ferns: $372 - $132 = $240. This is 2 equal shares, the cacti cost and the ferns cost without the extra.
- Total cost of the cacti = $240 ÷ 2 = $120.
- (b) Total cost of the ferns = $120 + $132 = $252.
- Ferns : cacti in number = 3 : 2, so split the plants into units: ferns 3 units, cacti 2 units.
- Cost of 1 unit of ferns = $252 ÷ 3 = $84. Cost of 1 unit of cacti = $120 ÷ 2 = $60.
- Each unit has the same number of plants, so the difference $84 - $60 = $24 comes from the $2 price difference.
- Number of plants in 1 unit = $24 ÷ $2 = 12.
- Cost of each fern = $84 ÷ 12 = $7.
The mistake this question tests
Stopped at one part in ratio
Many pupils work out $372 - $132 = $240 and call that the cost of the cacti, forgetting that $240 is two equal shares and must be halved. Others divide $252 by 3 and say each fern costs $84, forgetting that 1 unit has many plants.
How to fix it at home →More PSLE fractions questions
A zoo had 90 more visitors on Sunday than on Saturday
See the answer →Short answer · 2mA community centre kept exercise books in Box R and Box S
See the answer →Structured · 3mAt a night market, Stall X sold 2/3 of its keychains, Stall Y sold 1/4 of its keychains and Stall Z sold 1/2…
See the answer →Structured · 4mAt a science centre on a Saturday, the number of men is 1/3 of the number of women
See the answer →Structured · 4mClass 6B had 24 more pupils than Class 6A on a school camp
See the answer →Structured · 5mAt a school fair, Priya bought cans of soda and bottles of juice
See the answer →Practise PSLE fractions until the mistakes stop.
Three PSLE questions, free, no sign-up. You’ll see exactly where the marks went. Then 7 days of everything for S$4.99.