Estimation and Computation N5.1

Use front-end rounding to estimate the difference of:
7166 - 2998

• 10 000
• 5000
• 7000
• 4000

Estimate to find which two numbers have a sum of ABOUT 10 000

• 800 + 3950
• 8010 + 1627 
• 8243 + 3000
• 8847 + 200 

Estimate to find which two numbers have a difference of ABOUT 4000

• 80 916 - 59 978
• 10 832 - 2041
• 92 439 - 81 899
• 25 263 - 21 090

Use front-end rounding to estimate the sum of:
590 322 + 473 990

• 1 000 000
• 600 000
• 100 000
• 900 000

Which does NOT show using compatible numbers to estimate:
422 + 329

• 500 + 300 = 800
• 420 + 320 = 740
• 420 + 330 = 750
• 425 + 325 = 750

Which shows using COMPENSATION to estimate:
5425 - 3931

• 5000 - 3000 = 2000
• 6000 - 4000 = 2000
• 5400 - 3900 = 1500
• 5000 - 4000 = 1000

A student said that the estimated sum of 374 + 213 is 500.  What estimation strategy do you think the student use?

• front-end rounding (300 + 200)
• compatible numbers (370 + 210)
• compensation (

front-end estimation will always give an

• overestimate
• underestimate
• exact answer

Compatible numbers estimation can give 

• overestimate
• underestimate
• either an overestimate or underestimate depending on the chosen numbers

The estimated sum is 7000 . What might have the original numbers been?

• 5839 + 1219
• 4399 + 4921
• 6809 + 3061
• 5201 + 1327