How many three digits numbers are there in which all the digits a

SOLUTION

Short Trick:
There are 5 odd and 5 even numbers. So there are 5 possible values of each place. And there are 3 places. So total number of 3 digit numbers in which all the digits are odd = 5*5*5 = 125
Basic Explanation:
First odd number in which all the digits are odd is 111, and last one is 999
Let us see all such numbers starting from 1.
They are 111, 113, 115,117,119,131,133, 135, 137, 139, 151, 153, 155, 157, 159, 171, 173, 175, 177, 179, 191, 193, 195, 197, 199
So there are 25 odd numbers starting with 1 in which all digits are odd. So same for 3, 5, 7 and 9
Hence total odd number in which all the digits are odd are 25× 5=125