Question

Evaluate: $\left(i\right)69\times 71$, (ii) $94\times 106$.

Answer 1

Using $(a-b)(a+b)=a^2-b^2$
(i) $69\times 71$=(70-1)(70+1)
$=(70{)}^2-(1{)}^2=4900-1=4899$
(ii) $94\times 106$= (100-6)(100+6)
=$(100{)}^2-(6{)}^2$
=10000-36=9964