let's say the amount of people going is "p", whatever value "p" is, we know is more than 50, p > 50.
well, let's say that all of the folks are going in vans, we don't know how many vans are needed, we do know it'll be "k" vans, since each van can only carry 5 folks, the total amount of people going will fit in 5k vans.
let me put it differently, let's say we know 500 folks are going to the zoo, each van can only carry 5 folks each, so to be able to fit in 500 in vans, we need 500/5 = 100 vans, if we had 100 vans, each van carrying 5 folks each, that'll be a total of 500 people going in vans, so "k" will be 100, and the amount going will be 5k.
well, not everyone in "p", which is now 5k, p = 5k, is going together, 10 folks are driving themselves, so, <u>the people going to the zoo is, however many are going in the vans, 5k, plus the 10 driving on their own</u>, + 10, 5k + 10 are going to the zoo, and we know that's more than 50, 5k + 10 > 50.
