Worksheet: Estimating Sums of Three-Digit Numbers: Compatible Numbers

In this worksheet, we will practice using compatible numbers like 25, 50, 75, and 100 to estimate the value of sums up to 1000.

Q1:

Compatible numbers are pairs of numbers that are easy to add, subtract, multiply, or divide mentally.

First, calculate the actual sum of the following:

Second, use compatible numbers to estimate the sum of the following:

Q2:

Use compatible numbers to estimate 378+326.

  • A720
  • B705
  • C740
  • D760

Q3:

Use compatible numbers to estimate 177+226.

  • A500
  • B440
  • C403
  • D300
  • E400

Q4:

Pick the best estimate for this sum.

Hint: Use compatible numbers. 327+564

  • A900
  • B880
  • C890
  • D875

Q5:

Yesterday, Benjamin won 128 coins at the fair in the morning and 278 coins in the afternoon. Pick the best estimate for the total number of coins he won yesterday.

Hint: Use compatible numbers.

  • A410
  • B430
  • C450
  • D380

Q6:

Pick the best estimate for this sum.

Hint: Use compatible numbers. 232+581

  • A810
  • B850
  • C900
  • D890

Q7:

Pick the best estimate for 451+138.

Hint: Use compatible numbers.

  • A580
  • B600
  • C590
  • D550

Q8:

We can use compatible numbers to estimate sums.

Pick the calculation that best estimates this sum.

  • A425+200625
  • B425+235660
  • C400+200600
  • D450+250700

Q9:

Pick the best estimate for this sum.

Hint: Use compatible numbers. 781+123

  • A905
  • B800
  • C940
  • D960

Q10:

Pick the best estimate for this sum.

Hint: Use compatible numbers. 118+267

  • A395
  • B385
  • C375
  • D400

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