Question

Fill in the blank

$\begin{array}{ccc}7& 6& 21\\ 8& 5& 20\\ 12& 4& .....\\ a& b& c\end{array}$

Answer 1

In this problem, we observe that in' each row the last number is half the product of the first two numbers.
Formula : $\frac{a\times b}{2}=c$
$7\times 6=42;42÷2=21$
$8\times 5=40;40÷2=20$
$12\times 4=48;48÷2=24$