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

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## 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?

Video Solution
Surface-Areas-And-Volumes
Ex exercise-13-5 | Question 9

## 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}

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