Counting the Jelly Beans by Layers
At the school fair, Priya found a clear box packed with jelly beans, and a sign said, "Guess how many and win the box." Counting every bean was not allowed because the box was too full and the line behind her was growing.
Priya remembered a trick from math class, which is that when you cannot count everything, you estimate. An estimate is a smart guess that is close to the real answer. She began with one layer, and when she looked through the front she counted 5 beans across, and when she looked through the side she counted 4 beans deep. So one layer held about 5 times 4, which is 20 beans.
Next she counted the layers from the bottom to the top. There were 6. Now she multiplied again. Twenty beans in each layer times 6 layers is about 120 beans.
Priya knew her answer might not be exact because beans are not perfect squares and some of them bend into the gaps, but a guess of 120 was far better than a wild guess of 1,000 or 30. She wrote 120 on her slip.
When the fair ended, the winner was a boy who guessed 118. He had used the same layer trick. Priya was not upset. She had learned that a good estimate comes from breaking a big job into small, easy parts.