Estimating Sums and Differences — Let's Practise!

Estimating Sums and Differences — Let's Practise! exercise

• Place the estimates where they belong.

  Hints

  Remember, when we round numbers to the nearest 1,000, we look at the digit in the hundreds place. In 7,872 there is an 8 in the hundreds column, so we round up to 8,000.

  When rounding to the nearest 1,000, look at the digit in the hundreds column. In 5,098 there is a zero in the hundreds place, so we would round down to 5,000.

  Solution

  6,712 rounds up to 7,000

  3,298 rounds down to 3,000

  1,900 rounds up to 2,000

  1,004 rounds down to 1,000

• Estimate the digits and the sum to the nearest 1,000.

  Hints

  Remember, when we estimate we round a digit up or down based on the place value. For example, 5,930 would round to 6,000, because it is closer to 6,000 than to 5,000.

  7,324 would round down to 7,000, since it is closer to 7,000 than 8,000.

  Add the two estimates together to find the estimated sum.

  Solution

  4,071 rounds down to 4,000, and 4,913 rounds up to 5,000. Now we can estimate the sum: 4,000 + 5,000 = 9,000

• Fill in the missing numbers.

  Hints

  Round the numbers to the nearest 1,000.

  Remember to look at the digit in the hundreds column, if this is 5 or more we round up. If the hundreds digit is 4 or lower, we round down.

  For example, look at the number 5,321. If we want to round this to the nearest 1,000, we look at the digit in the hundreds column. This is a 3, so we round down to 5,000.

  Remember, the estimates should add up to 11,000.

  Solution

  6,646 rounds up to 7,000. 3,711 rounds up to 4,000.

  7,000 + 4,000 = 11,000

• Fill in the missing estimates.

  Hints

  Remember, we need to round the number to the nearest thousand.

  For example, 6,786 would round to 7,000, because there is a 7 in the hundreds column, so we round up.

  To find the total estimate, subtract the second estimate from the first.

  Solution

  8,598 rounds up to 9,000. 5,523 rounds up to 6,000.

  9,000 - 6,000 = 3,000

• Estimate the sum.

  Hints

  Remember to round each number to estimate the sum.

  Look at the number 3,754. Is it closer to 3,000, or to 4,000?

  Look at the number 4,213. Is it closer to 4,000, or 5,000?

  Solution

  We round 3,754 up to 4,000. Then, we round 4,213 down to 4,000.

  4,000 + 4,000 = 8,000

• Fill in the difference.

  Hints

  Remember, first round each number to the nearest thousand. Then, estimate the difference.

  Look at the number 4,798. When we round to the nearest 1,000 we look at the hundreds digit, if this is 5 or higher we round up. In 4,798 there is a 7 in the hundreds column, so we round up to 5,000.

  Solution

  12,421 rounds down to 12,000.

  6,882 rounds up to 7,000.

  12,000 - 7,000 = 5,000