WAEC 2019 · Paper 1 · Q26

Expressions, formulae & change of subject

Make $b$ the subject of the relation $lb = \frac12(a + b)h$ .

Worked solution (try it first)

Multiply by 2 and expand: $2lb = ah + bh$ .
Collect the $b$ terms: $2lb - bh = ah$ , so $b(2l - h) = ah$ .
Divide by $2l - h$ : $b = \dfrac{ah}{2l - h}$ , option A.

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