We are learning to estimate (aka round numbers) in order to make them easier to add, subtract, and multiply.
It's easier to work with rounded numbers because they end in zero (or for big numbers, lots of zeroes). The trick is to find a number with zeroes that it's very close to.
Think of it this way. If you wanted to figure out how much money it would cost to buy each of your 18 classmates a pack of pencils for 99 cents, would you rather multiply:
18 x $0.99
or
18 x $1?
It's easier to work with rounded numbers because they end in zero (or for big numbers, lots of zeroes). The trick is to find a number with zeroes that it's very close to.
Think of it this way. If you wanted to figure out how much money it would cost to buy each of your 18 classmates a pack of pencils for 99 cents, would you rather multiply:
18 x $0.99
or
18 x $1?
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