Answer :
Each student will collect 21 leaves (5+3+7+6). Therefore 18 x 21 = n or 18 x 21 = 378 leaves.
You can round the amount of leaves to about 20 and the amount of people to about 20 to get an estimate of about 400 leaves. 20 x 20 is a simple problem that doesn't need a calculator. 400 is very reasonably close to 378.
You can round the amount of leaves to about 20 and the amount of people to about 20 to get an estimate of about 400 leaves. 20 x 20 is a simple problem that doesn't need a calculator. 400 is very reasonably close to 378.