Question

The number of students in class 20 minutes ago was 729 . If the number of students joining the class triples every 10 minutes, what is the cube root of the number of students joining after 40 minutes from now?

• A. 81
• B. 27
• C. 64
• D. 48

Answer 1

The correct option is A

81

For every 10 mins passage of time, the number of students joining the class gets tripled i.e. multiplied by 3

The number of students joining after 40 minutes from now on is $729\times 3\times 3\times 3\times 3\times 3\times 3$ ( from 20 mins back to 40 mins forward)

The cube root of 729 is 9.

Cube root of given number is $9\times 3\times 3=81$