Question 14

Multiply 20 by 20 and subtract 4 × 4.

This method effectively simplifies the multiplication problem by using rounding and basic arithmetic. By multiplying 20 by 20 to get 400 and then subtracting 16, which is the product of 4 and 4, the calculation becomes straightforward.

A) Multiply 20 by 20 and subtract 4 × 4.

This option is correct because it uses a rounding technique to simplify the multiplication. By calculating 20 × 20, we obtain 400. Then, subtracting 16 (which is 4 × 4) gives us the correct product of 384 for 24 × 16.

B) Multiply 20 by 20.

This option is incorrect because while multiplying 20 by 20 yields 400, it does not provide the correct answer for 24 × 16. The complete calculation requires additional steps to adjust for the difference between 24 and 20.

C) Multiply 20 by 10 and add 4 × 6.

This option is incorrect as it does not relate directly to the multiplication of 24 by 16. The calculation of 20 × 10 gives 200, and adding 24 (from 4 × 6) results in 224, which is far from the correct product.

D) Multiply 25 by 10 and add 4 × 15.

This option is also incorrect. Although multiplying 25 by 10 gives 250, adding 60 (from 4 × 15) results in 310, which does not correspond to the product of 24 and 16.

Conclusion

Option A is definitively the correct method for quickly multiplying 24 by 16 as it effectively utilizes rounding and subtraction to arrive at the accurate product. The other options fail to either reach the correct total or do not provide a viable method for simplifying the calculation. Thus, A stands out as the best strategy for this multiplication problem.