Question

while writing all 5 digit
numbers, How many times will we write 7?
​

Answer 1

Step-by-step explanation:

3700

Let us call the 4 digit number as abcd

When a = 2, b / c / d can be filled in 10 ways each.

So, 2 will appear in place of 'a' 10*10*10 = 1000 times

When b = 2, a can be filled in 9 ways whereas c / d can be filled in 10 ways each.

So, 2 will appear in place of 'b' 9*10*10 = 900 times

Similarly, 2 will appear in place of 'c' 900 times and in place of 'd' 900 times.

Total number of times digit '2' will appear = 1000 + 900 + 900 + 900 = 3700 times