Question

Find the next number in the series 125, 80, 45, 20, ....

• A. 15
• B. 5
• C. -10
• D. -5

Hint:

Try writing each term as 5 times a perfect square.

Answer 1

The Correct Option is B

Rewrite each term as $5$ times a perfect square: $125 = 5(5^2)$, $80 = 5(4^2)$, $45 = 5(3^2)$, $20 = 5(2^2)$.
The square term drops by 1 each time: $5,4,3,2$, so the next square term is $1$.
Next number $= 5(1^2) = 5$.
\[\boxed{5}\]