Angelina and Brad are both running for class president….

Question

Angelina and Brad are both running for class president. Angelina goes down a hallway in the school and puts a sticker on every 28 lockers. Brad goes down the same hallway, putting one of his stickers on every 20 lockers. If there are 420 lockers in the hallway, how many have both students' stickers?

Answer 1

Assume that the first locker has neither campaign sticker.

Look for the values of i where the i^th locker has both campaign stickers.

i must be divisible by both 20 and 28 which means each 5th locker that has Angelina's campaign sticker will have Brad's campaign sticker

 

420/28 = 15 is the number of lockers that will have Angelina's campaign sticker

Therefore only 3 lockers will have both campaign stickers where i = 5, 10, and 15