Estimating with Compatible Numbers
Use friendly numbers to estimate sums, differences, products, and quotients
Estimating with Compatible Numbers
Use friendly numbers to estimate sums, differences, products, and quotients
Math - Grade 4-5
- 1
Estimate 398 + 204 using compatible numbers. Explain which numbers you used.
Look for numbers that are close to hundreds.
398 is close to 400, and 204 is close to 200. So 398 + 204 is about 400 + 200 = 600. - 2
Maya has 487 stickers, and her friend gives her 312 more. Use compatible numbers to estimate how many stickers Maya has now.
487 is close to 500, and 312 is close to 300. Maya has about 500 + 300 = 800 stickers. - 3
Estimate 721 - 298 using compatible numbers. Show your thinking.
Choose numbers that make subtraction easy.
721 is close to 700, and 298 is close to 300. So 721 - 298 is about 700 - 300 = 400. - 4
A school library has 1,206 books. Students check out 398 books. Estimate how many books are left using compatible numbers.
1,206 is close to 1,200, and 398 is close to 400. There are about 1,200 - 400 = 800 books left. - 5
Estimate 49 x 21 using compatible numbers. Explain your estimate.
Round to numbers that end in zero.
49 is close to 50, and 21 is close to 20. So 49 x 21 is about 50 x 20 = 1,000. - 6
A bus holds 38 students. About how many students can ride on 9 buses? Use compatible numbers.
38 is close to 40, and 9 is already easy to use. About 40 x 9 = 360 students can ride on 9 buses. - 7
Estimate 2,412 ÷ 6 using compatible numbers. Show how you chose your numbers.
Choose a nearby number that divides evenly by 6.
2,412 is close to 2,400, and 2,400 divides evenly by 6. So 2,412 ÷ 6 is about 2,400 ÷ 6 = 400. - 8
A farmer packs 1,785 apples equally into 9 boxes. Estimate how many apples are in each box using compatible numbers.
1,785 is close to 1,800, and 1,800 divides evenly by 9. Each box has about 1,800 ÷ 9 = 200 apples. - 9
Choose the better compatible number estimate for 603 + 198: 600 + 200 or 500 + 100. Explain your choice.
The best compatible numbers should stay close to the original numbers.
600 + 200 is the better estimate because 603 is close to 600 and 198 is close to 200. The estimate is 800. - 10
Estimate 4,089 - 1,987 using compatible numbers.
4,089 is close to 4,100 or 4,000, and 1,987 is close to 2,000. One good estimate is 4,100 - 2,000 = 2,100. - 11
A theater sold 52 tickets for each of 18 shows. Estimate the total number of tickets sold using compatible numbers.
Use numbers that make multiplication quick.
52 is close to 50, and 18 is close to 20. The theater sold about 50 x 20 = 1,000 tickets. - 12
A student estimates 3,152 ÷ 8 by using 3,200 ÷ 8. Is this a good compatible number estimate? Explain why or why not.
A compatible number should be close to the original number and easy to divide.
Yes, this is a good estimate because 3,200 is close to 3,152 and divides evenly by 8. The estimate is 3,200 ÷ 8 = 400.