SEAMO 2027 - Paper E - SET 04 - Self-study Question 24

Let $N=3^a+7^b$, where integers $a,b$, not necessarily different, are chosen uniformly at random from 1 through 100 inclusive. Find the probability that the units digit of $N$ is 4.

Practice interpretation: a and b are selected independently; equal values are allowed, as the source states. Uniform marginal choices alone would not determine the joint probability.