Estimating and Modeling Decimal Sums and Differences

Round to the nearest WHOLE number to find the sum: 34.87 + 20.41

• 55

• 55.28

• 54

• 50

Round to the nearest WHOLE number to find the sum:

44.56 + 14.72

• 59.28

• 50

• 60

• 58

Round to the nearest TEN to find the sum:

19.36 + 12.88

• 32.24

• 31

• 32

• 30

Round to the nearest WHOLE number to find the difference:

324.61 - 211.87

• 113

• 112.74

• 100

• 110

Round to the nearest HUNDRED to find the difference:

576.76 - 231.84

• 200

• 300

• 400

• 344.92

Estimating is finding a value that is CLOSE or APPROXIMATE to the actual value, but it's not exact.

• True

• False

Roughly, approximately, and about are all clues for knowing when to round or estimate.

• True

• False

What is the symbol used when rounding/estimating?

• ≈

• =

• *

• #

What are compatible numbers?

• Two of the same numbers.

• Numbers that have the same digit in the ones place.

• Pairs of numbers that are easy to add, subtract, multiply, or divide mentally.

• Numbers that have the same amount of digits.

Choose a good pair of compatible numbers to make finding the sum of 223.4 + 148.9 easier to add mentally.

• 200 + 100

• 223 + 149

• 225 + 150

• They're already compatible.