Question

A two-digit random number is chosen. What is the probability that the sum of its digits is 5?

Answer 1

There are 90 two digit numbers.
The numbers that have 5 as the sum of their digits are:
14,23,32,41,50
which are 5 numbers out of the possible 90

Therefore the probabilty is 5/90 or 1/18

Answer 2

10≤n<100

So the number of two digit numbers is 99-10+1=90

The only combinations that sum to 5 are 14, 23, 32, 41, 50 so

P(sum=5)=5/90

P(sum=5)=1/18