Question

$\begin{array}{ccc}20& 12& 42\\ 6& 30& 2\\ ....& 90& 72\end{array}$

• A. 56
• B. 22
• C. 36
• D. 44

Answer 1

Answer: (A)

56

Arrange the number in the ascending order.
$2=1^2+1;2^2-2$
$6=2^2+2;3^2-3$
$12=3^2+3;4^2-4$
$20=4^2+4;5^2-5$
$30=5^2+5;6^2-6$
$42=6^2+6;7^2-7$
$72=8^2+8;9^2-9$
$90=9^2+9;{10}^2-10$
Formula : $n^2+n\left(or\right)n^2-n$
The missing numbers is $7^2+7(or{8}^2-8)=56$