JAMB 1988 · UME · Q2

Number foundations & fractions

If $x$ is the sum of the prime numbers between 1 and 6, and $y$ is the H.C.F. of 6, 9 and 15, find the product of $x$ and $y$ .

Worked solution (try it first)

The prime numbers between 1 and 6 are 2, 3 and 5, so $x = 2 + 3 + 5 = 10$ .
The largest number that divides 6, 9 and 15 is 3, so $y = 3$ .
So $xy = 10 \times 3 = 30$ , option B.

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