Lesson 6 of 14
Estimate before you compute
Show on a big screenA friend says 1,480 × 260 = 38,48,000. Check the size before you trust it.
Step 1 of 4
- Job: 1,480 × 260. Round to 1,500 × 300.
- Estimate: 4,50,000.
- Keep answers between 2,25,000 and 9,00,000.
- 38,48,000 is too big. 3,84,800 fits.
The friend's answer is too big.
The rule
Round both numbers to the same place. Pick a place no bigger than half the smaller number. Multiply the rounded pair. The product is your estimate. An estimate is near the answer, not equal to it. A right answer is between half the estimate and double it.
Round to the nearest hundred: 1,500 × 300 = 4,50,000. Half of that is 2,25,000. Double of that is 9,00,000. The friend's 38,48,000 is above 9,00,000, so it is wrong. The real answer, 3,84,800, is between 2,25,000 and 9,00,000.
Tap the answer that can be right in the lab. The lab shows the estimate.
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Try the lab to finish this lesson.