JAMB 1992 · UME · Q6

Simplify $5\sqrt{18} - 3\sqrt{72} + 4\sqrt{50}$ .

Worked solution (try it first)

Take out square factors: $5\sqrt{18} = 5 \times 3\sqrt2$ , which is $15\sqrt2$ .
Likewise $3\sqrt{72} = 3 \times 6\sqrt2 = 18\sqrt2$ and $4\sqrt{50} = 4 \times 5\sqrt2 = 20\sqrt2$ .
Combine the like surds: $15\sqrt2 - 18\sqrt2 + 20\sqrt2 = 17\sqrt2$ , option C.