Question

Someone listed all the numbers from 0 to 99999 in increasing order. Then he crossed out all the numbers where some other digit(s) besides 0 and 1 were used. A How many numbers does he have left?

Answer 1

Answer: he has 32 numbers left.

Step-by-step explanation:

The first given number is 0.

1-digit number 1 *1 (=1)

2-digit numbers (1 and , 2 choices for 2nd digit). 1*2 (= 2)

3-digit numbers ( 1, 2 and first choice for 3.). 1*2*2 (= 4)

4-digit numbers (we join our answer for 1,2 and 3 with first choice of 4). 1*2*2*2 (= 8)

5-digit numbers s (1, 2, 3rd, 4th & first Choice of 5th digits). 1*2*2*2*2 (= 16)

Total number range from 0 to 1.

1 + 1 + 2 + 4 + 8 + 16

= 2^5

= 32.