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Hi there! Today we will learn how to round numbers to estimate answers quickly.
Sometimes we do not need an exact number. We can estimate to find a quick, close answer.
To round to the nearest ten, look at the ones place. If it is 5 or more, round up!
We can also use compatible numbers. These are friendly numbers that are very easy to add or subtract in your head.
✏️ Worked example
Sam has 42 red marbles and 37 blue marbles. Estimate how many marbles Sam has in total by rounding to the nearest ten.
- Find the number of red marbles. There are 42 red marbles.
- Look at the ones place of 42. Since 2 is less than 5, we round down to 40.
- Find the number of blue marbles. There are 37 blue marbles.
- Look at the ones place of 37. Since 7 is 5 or more, we round up to 40.
- Add the two rounded numbers together: 40 + 40 = 80.
- So, Sam has about 80 marbles in total!
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