math
posted by peter .
at a grand opening of a store, every 3rd person is given a balloon, and every 7th person is given a $5 coupon. if a person is selected at random from the first 100 people to shop there, whats the probability that the person will be given a balloon and a coupon?
how do you do this problem?

IT must occur on the 21st, 42nd, 63rd, 84th persons.
Pr= 4/100