# Ex.13.5 Q9 Surface Areas and Volumes Solution - NCERT Maths Class 9

## Question

A river \(3\rm m\) deep and \(40 \rm m\) wide is flowing at the rate of \(2 \rm km\) per hour. How much water will fall into the sea in a minute?

## Text Solution

**Reasoning:**

Water that falls in to the sea in the volume of the cuboid.

**What is known?**

Depth, wide and rate of water following per hour.

**What is unknown?**

Amount of water will fall in to the sea in a minute.

**Steps:**

length \((l) \!=\! 2\,\rm km \!=\! 2 \!\times\! 1000 \!=\! 2000\,\rm m \)

breadth \((b) = 40\,\,\rm m \)

height \((h) = 3\,\,\rm m \)

Water fall in the sea \(=\) Volume of cuboid \( = l\times b\times h\)

\[\begin{align} = 2000 \times 40 \times 3 \end{align}\]

This is for \(1\) hour

Therefore, water fell in to the sea in a minute.

\[\begin{align} &= \frac{{2000 \times 40 \times 3}}{{60}}\\ &= 4000\,\,\rm{m^3} \end{align}\]

**Answer:**

\(\begin{align}4000\,\,\rm{m^3} \end{align}\) of water will fall into the sea in a minute.