WAEC 2021 · Paper 1 · Q9

Linear & simultaneous equations

Mensah is 5 years old and Joyce is thrice as old as Mensah. In how many years will Joyce be twice as old as Mensah?

Worked solution (try it first)

Joyce is three times Mensah's age: $3 \times 5 = 15$ years old.
In $n$ years they will be $5 + n$ and $15 + n$ .
Joyce is then twice Mensah's age: $15 + n = 2(5 + n)$ .
Expand: $15 + n = 10 + 2n$ .
Take $n$ and 10 from both sides: $n = 5$ .
So in 5 years (ages 10 and 20), option C.

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