Using Compatible Numbers to Multiply & Divide
Resource Overview Quantile® Measure:
690Q
Skill or Concept:
Estimate and compute products of whole numbers with 2‐ or 3‐digit factors. (QT‐N‐170) Estimate and solve division problems with 2‐ and 3‐digit divisors; explain solution. (QT‐N‐171)
Excerpted from:
The Math Learning Center PO Box 12929, Salem, Oregon 97309‐0929 www.mathlearningcenter.org © Math Learning Center
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Set A3 Number & Operations: Estimating to Multiply & Divide Blackline Run a class set.
name
date
Set A3 H Independent Worksheet 1 Independent Worksheet
Using Compatible Numbers to Multiply & Divide Mathematicians sometimes estimate answers to multiplication and division problems by using compatible numbers. Compatible numbers are numbers that work well together.
example 1
A page in my chapter book has 12 words in each line and 32 lines on the page. About how many words on the whole page? Change 12 and 32 to nearby numbers that are easier to multiply in your head.
example 2
Mr. Gomez had 396 crayons left over at the end of the year. He’s putting them in bags to send home with the kids. He has 20 students in his class. About how many crayons will each student get? Change 396 to a nearby number that is easier to divide by 20.
12 is close to 10 32 is close to 30 396 is close to 400. 10 x 30 = 300, so the page has about 300 words. 20 is already a friendly number. You don’t always have to change both numbers. 400 ÷ 20 = 20, so each student will get about 20 crayons.
1
Choose a chapter book from your classroom. Turn to a page in the middle of the book. About how many words do you think there are on the page? To find out, count the number of words in one line. Next, count the number of lines on the page. Record the information: Words in one line _______________
Lines on the page ________________
2
Use compatible numbers to estimate the number of words on the page. Show your work.
(Continued on back.) © The Math Learning Center
Bridges in Mathematics Grade 5 Supplement • A3.1
Set A3 Number & Operations: Estimating to Multiply & Divide Blackline Run a class set.
Independent Worksheet 1 Using Compatible Numbers to Multiply & Divide (cont.)
3
All the fourth and fifth graders at King School are going on a field trip with their teachers and some parent helpers. In all, there will be 197 people. The bus company plans to use 4 buses. Estimate how many people will ride in each bus. Use compatible numbers to help you. Show your work.
4
Use compatible numbers to estimate the answer to each problem below. To use this estimation strategy, change the actual numbers to nearby numbers that are compatible. The first two are done for you.
multiplication example
21 × 19
division example
249 ÷ 24
20 21 is close to _______.
250 249 is close to _______.
20 19 is close to _______.
25 24 is close to _______.
400 20 × _______ 20 _______ = _______,
10 250 ÷ _______ 25 _______ = _______,
400 so the answer is about _______.
10 so the answer is about _______.
a
b
32 × 29
153 ÷ 9
32 is close to _______.
153 is close to _______.
29 is close to _______.
9 is close to _______.
_______ × _______ = _______,
_______ ÷ _______ = _______,
so the answer is about _______.
so the answer is about _______.
c
d
49 × 19
119 ÷ 9
49 is close to _______.
119 is close to _______.
19 is close to _______.
9 is close to _______.
_______ × _______ = _______,
_______ ÷ _______ = _______,
so the answer is about _______.
so the answer is about _______.
A3.2 • Bridges in Mathematics Grade 5 Supplement
© The Math Learning Center
