You are a landscaper and need to mulch 15 yards of plant beds. you have 20 bags of mulch and each bag covers 3 feet.

Whats the question?

You'll need 15 bags to cover 15 yards
1 bag/ 3 feet
3 feet/ 1 yard

15 bags = 45 feet = 15 yards

You have 20 yards of mulch because each bag covers one yard. Remember that there are three feet in one yard. (3 ft. = 1 yd.) If each bag covers three feet then each bag covers one yard of plant bed. If you have 20 bags and each contains one yard of mulch, then you would have plenty of mulch to cover all of the plant beds. You would even have 5 yards or 5 bags of mulch left over.