How many numbers are there between 100 and 1000 such that every digit

1.	How many numbers are there between 100 and 1000 such that every digit is either 2 or 9?
Answer» Any number between 100 and 1000 is of 3 digits. The unit’s place can be filled by 2 or 9 in 2 ways. Similarly ten’s place can be filled in 2 ways. The hundred’s place can also be filled in 2 ways. ∴ Required no. of numbers = 2 × 2 × 2 = 8.

How many numbers are there between 100 and 1000 such that every digit is either 2 or 9?

Answer»

Any number between 100 and 1000 is of 3 digits. The unit’s place can be filled by 2 or 9 in 2 ways.

Similarly ten’s place can be filled in 2 ways.

The hundred’s place can also be filled in 2 ways.

∴ Required no. of numbers = 2 × 2 × 2 = 8.