# Find the missing term in 3×3 table

8 10 9
? 15 28
7 12 13

A) 9 B) 10 C) 11 D) 12

C)11

Please explain how to solve this question?

Source: NTSE stage 1 rajasthan 2012.

the number of prime factors.

Let's examine the numbers in the grid:

7 = 7
8 = 2 × 2 × 2
9 = 3 × 3
10 = 2 × 5
12 = 2 × 2 × 3
13 = 13
15 = 3 × 5
28 = 2 × 2 × 7

There are :
- 2 numbers with one prime factor (i.e 2 prime numbers)
- 3 numbers with two prime factors
- 3 numbers with three prime factors

Therefore, the ? should be replaced with

a prime number. Answer C) is the only one.