Which calculation does NOT give the benchmark estimate of 40 for 7.9 × 5.2?

الشرح

Rounding the factors gives 8 × 5 = 40, and equivalent benchmark products such as 16 × 2.5 and 4 × 10 also equal 40. The calculation 8 + 5 = 13 adds the rounded values and therefore does not estimate the product.