What is the probability that this problem is interesting?

Discrete Mathematics Level 3

Pi Han randomly chooses two distinct integers from the set of integers \(\{1,2,3,4 \dots 99,100\}\). Let the ratio of the first number to second number chosen be \(R\). If the probability that \(R<1\) can be expressed as \(\dfrac{a}{b}\) for co-prime integers \(a,b\) , Find \(a+b\)