Question

Tick (✓) the correct answer:
(197 × 203) = ?
(a) 39991
(b) 39999
(c) 40009
(d) 40001

Answer 1

(a) 39991

$$\begin{gathered} \left(197\right)\times \left(203\right) \\ \Rightarrow \left(200-3\right)\left(200+3\right) \\ \Rightarrow {\left(200\right)}^2-{\left(3\right)}^2 \\ \Rightarrow 40000-9 \\ \Rightarrow 39991 \end{gathered}$$ [using the identity (a+b) (a-b) = a² -b²]