Estimating Sums: The Lemonade Stand

Business is busy at the Lemonade Stand! Zoe and Mia don’t always need the exact number of cups. To know about how many, they round each number and add the round numbers in their heads.

Remember: Estimate a sum: round each number, then add. 48 + 31 is about 50 + 30 = 80. For bigger numbers, round to the nearest hundred: 456 + 387 is about 500 + 400 = 900. An estimate is close, not exact, so we say about.

Magic trick: Round first, add second. Round numbers are friendly: 50 + 30 is as easy as 5 + 3.