JAMB 1997 · UME · Q2

Evaluate $64.764^2 - 35.236^2$ correct to 3 significant figures.

Worked solution (try it first)

Use the difference of two squares: $a^2 - b^2 = (a - b)(a + b)$ .
Here $a - b = 64.764 - 35.236 = 29.528$ and $a + b = 100$ , so the value is $29.528 \times 100 = 2952.8$ .
To 3 significant figures, the fourth figure is 2, so round down: 2950, option B.