Estimate 39 × 42 by rounding to the nearest ten.

Estimate 39 × 42 by rounding to the nearest ten.

• A. 1500
• B. 1680
• C. 1600
• D. 1700

Answer: (C)

Rounding to the nearest ten to estimate a product means replacing each factor with a nearby multiple of ten and multiplying the simpler numbers. Round 39 to 40 and 42 to 40. Then multiply 40 by 40 to get 1600. This is a sensible estimate because the actual product is 39 × 42 = 1638, which sits between 1600 and 1700 and is closer to 1600. Using both numbers rounded to the nearest ten gives the best straightforward estimate here, so 1600 is the most reasonable choice.

Rounding to the nearest ten to estimate a product means replacing each factor with a nearby multiple of ten and multiplying the simpler numbers.

Round 39 to 40 and 42 to 40. Then multiply 40 by 40 to get 1600. This is a sensible estimate because the actual product is 39 × 42 = 1638, which sits between 1600 and 1700 and is closer to 1600. Using both numbers rounded to the nearest ten gives the best straightforward estimate here, so 1600 is the most reasonable choice.