The choices you offer are
4*19 = 76
4*20 = 80
5*19 = 95
5*20 = 100
Rounding both numbers to the nearest integer will give you the last result, 100. The actual product is slightly less than 95, so 5*19 turns out to give a more accurate estimate.
In most cases, the use of 5*20 = 100 as the estimate would be preferred for its simplicity. An error estimate would show this to be high by about 7 1/2%.
4*19 = 76
4*20 = 80
5*19 = 95
5*20 = 100
Rounding both numbers to the nearest integer will give you the last result, 100. The actual product is slightly less than 95, so 5*19 turns out to give a more accurate estimate.
In most cases, the use of 5*20 = 100 as the estimate would be preferred for its simplicity. An error estimate would show this to be high by about 7 1/2%.
