Question

How do I find an estimate for the sum of the numbers `622,78,81,111`, to the nearest `10`.?

Answer 1

`620 + 80 + 80 + 110 = 890`

Explanation:

When we're rounding any number to the nearest ten, we'll want to first find the two tens that it's in between.

For our problem:

• `622` is between `620` and `630`
• `78` is between `70` and `80`
• `81` is between `80` and `90`
• `111` is between `110` and `120`

Next, we want to find which of those tens each number is closest to. We'll round the number to that particular ten.

• `622` is closer to `620` than `630`, so we round it to `620`
• `78` is closer to `80` than `70`, so we round it to `80`
• `81` is closer to `80` than `90`, so we round it to `80`
• `111` is closer to `110` than `120`, so we round it to `110`

Finally, we can use our rounded addends to find an estimated sum:

`620+80+80+110=890`

Answer 2

`620," "80," "80," "110`

Explanation:

If a number is to be rounded to the nearest `10`, the answer must be a multiple of `10`. The last digit must be a `0`

To decide whether to round up or down, look at the digit in the units place. If it is `5` or more, round up. If it is `4` or less, round down.

`622 " " rarr 620`

`78 " "rarr 80`

`81 " "rarr 80`

`111" "rarr 110`