91Ó°ÊÓ

From given information, we came to know that,

Rate of printing black and white document$=8$pages/min

$8$pages $→$ $1$min.

Dividing with $8$on both sides, we get

$⇒$$\frac{8}{8}$pages $→$ $\frac{1}{8}$min.

$⇒$$1$page $→$ $\frac{1}{8}$min.

For printing $40$pages.

Let time be x.

$⇒$$40$pages $→$xmin --------(1)

Multiplying with $40$on both sides

We get

$⇒$$40$page $→$ $\frac{1}{8}×40$min -------(2)

Comparing equation-(1) and (2), we get

$x=\frac{40}{8}$

Multiplying with $8$on both sides, we get

$\begin{array}{c}8×x=\frac{40}{8}×8\\ 8×x=40\\ 8x=40\end{array}$

Therefore, required equation is $8x=40$.

On solving, we get

$x=\frac{40}{8}=5$min.

Equation is $8x=40$ and time taken to print 40 page of black and white documents is $5minute$

From given information, we came to know that,

Rate of printing color document $=5$pages/min

$5$pages $→$ $1$min.

Dividing with $5$on both sides, we get

$⇒$$\frac{5}{5}$pages $→$ $\frac{1}{5}$min.

$⇒$$1$page $→$ $\frac{1}{5}$min.

For printing $20$pages, let time be x.

$⇒$$20$pages $→$xmin --------(1)

Multiplying with $20$on both sides

We get

$⇒$$20$pages $→$$\frac{1}{5}×20$min---------------(2)

Comparing equation-(1) and (2), we get

$x=\frac{20}{5}$

Multiplying with $5$on both sides, we get

$\begin{array}{c}5×x=\frac{20}{5}×5\\ 5×x=20\\ 5x=20\end{array}$

Therefore, required equation is $5x=20$.

On solving, we get

$x=\frac{20}{5}=4$min.

Equation is $5x=20$ and time taken to print 40 page of black and white documents is $\text{4 minutes}$.

Total time taken to print both documents = Time taken to print black and white document +Time taken to print color document.

On substituting values, we get

$⇒$ Total time taken to print both documents $=5+4$

$⇒$ Total time taken to print both documents $=9$minutes.

Therefore, total time to print both documents $=9$minutes.