Make the given changes in the indicated examples of this section, and then solve the given problems.

In Example 13, change 12.9 to 21.9 and then find the estimated value.

Data from Example 13

In Example 1, we found that 38.3 − 12.9(−3.58) = 84.482 using exact numbers When using the calculator, if we forgot to make 3.58 negative, the display would be −7.882, or if we incorrectly entered 38.3 as 83.3, the display would be 129.482. However, if we estimate the result as 40 − 10(−4) = 80 we know that a result of −7.882 or 129.482 cannot be correct. When estimating, we can often use one-significant-digit approximations. If the calculator result is far from the estimate, we should do the calculation again.