CAT 2020

Slot 2

QA

Question & Solution

Here there are two cases possible

Case 1: When 7 is at the left extreme

In that case 3 can occupy any of the three remaining places and the remaining two places can be taken by $\text{(0, 1, 2, 4, 5, 6, 8, 9)}$

So total ways 3(8)(7)= 168

Case 2: When 7 is not at the extremes

Here there are 3 cases possible. And the remaining two places can be filled in 7(7) ways.

(Remember 0 can't come on the extreme left)

Hence in total $3(7)(7)$ = 147 ways

Total ways $168 + 147 = \boxed{\text{315 ways}}$