WAEC 2019 · Paper 1 · Q4

Simplify, correct to three significant figures, $(27.63)^2 - (12.37)^2$ .

Worked solution (try it first)

Use the difference of two squares: $a^2 - b^2 = (a - b)(a + b)$ .
Here $a - b = 27.63 - 12.37 = 15.26$ and $a + b = 40$ , so the value is $15.26 \times 40 = 610.4$ .
To 3 significant figures the 0 is the third figure and the next figure is 4, so round down: 610, option D.