To solve the question, first find the number of odd numbers from 1 to 25 and they are:(1,3,5,7,9,11,13,15,17,19,21,23,25)=13 There are 13 odd numbers from 1 to 25.
The probability that the first number is an odd is 13/25
Since the first ball wasn't placed back, 24 balls were left. There are 12 odd numbers from 1 -24
so the probability that the second number is odd is 12/24=1/2
13/25+1/2=51/52
