Question

A person starts writing all 4 digits numbers.How many times had he written the digit 2? ( 2 marks )

Answer 1

Answer:

3700

Step-by-step explanation:

Give us a chance to call the 4 digit number as abcd  

At the point when a = 2, b/c/d can be filled in 10 different ways each.  

Thus, 2 will show up instead of 'a' 10*10*10 = 1000 times  

At the point when b = 2, a can be filled in 9 different ways though c/d can be filled in 10 different ways each.  

Thus, 2 will show up instead of 'b' 9*10*10 = 900 times  

Likewise, 2 will show up instead of 'c' 900 times and instead of 'd' 900 times.  

Complete number of times digit '2' will show up = 1000 + 900 + 900 + 900 = 3700 times