A store is giving away a $10 dollar coupon to every 7th person to enter the store and a $25 coupon to every 18th person to enter the store.
To find the first person to get both coupons, you have to find the LCM of 7 and 18. First list the multiples of each number.
7 - 7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84, 91, 98, 105, 112, 119, 126, 133
18 - 18, 36, 54, 72, 90, 108, 126, 144
The common multiples are bold. The 126th person will be the first to get both coupons.