Question

Question 124 (i)

Evaluate the following, using distributive property.
$-39\times 99$

Answer 1

$-39\times 99=(-40+1)\times (100-1)=-40\times (100-1)+1\times (100-1)$
Now, using distributive property,
$=(-40\times 100)+(-1\times -40)+(1\times 100)+(1\times (-1\left)\right)[\because a\times (b\times c)=a\times b+a\times c]=-4000+40+100-1=-3861$