Answer
Estimated answer = 6
Exact answer = $6\frac{17}{20}$
Work Step by Step
$11\frac{9}{20}$ - $4\frac{3}{5}$
Estimation:
$11\frac{9}{20} \approx 11$
$4\frac{3}{5} \approx 5$
Therefore
$11\frac{9}{20}$ - $4\frac{3}{5}$ $\approx$ 11 - 5 = 6
Exact Calculation:
$11\frac{9}{20}$ - $4\frac{3}{5}$
= $11\frac{9}{20}$ - $4\frac{3\times4}{5\times4}$
(20 is the least common denominator)
= $11\frac{9}{20}$ - $4\frac{12}{20}$
= $11$ + $\frac{9}{20}$ - ($4$ + $\frac{12}{20})$
= $11$ + $\frac{9}{20}$ - $4$ - $\frac{12}{20}$
= ($11$ - $4$) + ($\frac{9}{20}$ - $\frac{12}{20}$)
(Solving whole parts separately and fractional parts separately)
= $7$ + $\frac{9 - 12}{20}$
= $7$ + $\frac{-3}{20}$
= $6+1$ - $\frac{3}{20}$
= $6$ + $\frac{20}{20}$ - $\frac{3}{20}$
= $6$ + $\frac{20 - 3}{20}$
= $6$ + $\frac{17}{20}$
= $6\frac{17}{20}$
The estimate was 6, so the exact answer of $6\frac{17}{20}$
is reasonable.
