WAEC 2012 · Paper 2 · Q5

(a)
A trader bought an article in Sierra Leone at Le 360,000. He paid $25\%$ of the cost price as import duty on entering Nigeria. If the rate of exchange is ₦1.00 = Le 16.00, how much, in naira, did he pay as import duty?
(b)
The mean of marks scored by 3 students in a test is 9. If the modal mark is 11, find the lowest mark.

Worked solution (try it first)

(a)

Import duty $= 25\%$ of Le 360,000 $=$ Le 90,000.
At ₦1.00 = Le 16.00, divide by 16 to change leones to naira: $90\,000 \div 16 = 5625$ , so the duty is ₦5,625.

(b)

The mean of 3 marks is 9, so the marks add up to $3 \times 9 = 27$ .
The mode is 11, so 11 appears more than once.
It can't appear three times ( $3 \times 11 = 33$ , not 27), so exactly two marks are 11.
The third mark is $27 - 11 - 11 = 5$ , and it's the lowest.

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