Answer
Estimated answer = 9
Exact answer = $9\frac{9}{40}$
Work Step by Step
$15\frac{7}{20}$ - $6\frac{1}{8}$
Estimation:
$15\frac{7}{20} \approx 15$
$6\frac{1}{8} \approx 6$
Therefore
$15\frac{7}{20}$ - $6\frac{1}{8}$ $\approx$ 15 - 6 = 9
Exact Calculation:
$15\frac{7}{20}$ - $6\frac{1}{8}$
= $15\frac{7\times2}{20\times2}$ - $6\frac{1\times5}{8\times5}$
(40 is the least common denominator)
= $15\frac{14}{40}$ - $6\frac{5}{40}$
= $15$ + $\frac{14}{40}$ - ($6$ + $\frac{5}{40})$
= $15$ + $\frac{14}{40}$ - $6$ - $\frac{5}{40}$
= ($15$ - $6$) + ($\frac{14}{40}$ - $\frac{5}{40}$)
(Solving whole parts separately and fractional parts separately)
= $9$ + $\frac{14 - 5}{40}$
= $9$ + $\frac{9}{40}$
= $9\frac{9}{40}$
The estimate was 9, so the exact answer of
$9\frac{9}{40}$ is reasonable.
