Question

- Clare removed marbles from a container of

water. When she removed 2 marbles, the
water level was 80 ml. When she removed
4 more marbles, the water level was 40 ml.
Write an equation for the water level y after
x marbles are removed.

Answer 1

y = 100 - 10x

Explanation:

Let y₀ be the original water level before any marbles were removed

Let y = water level after x marbles are removed.

Let d be the water level drop for every marble removed

Then we have the general equation:

y = y₀ - x.d

We have to find d and y₀

So we get one equation for the water level after removal of 2 marbles

80 = y₀ - 2d [1]

After 4 more marbles were removed, the water level drops to 40ml. That means for 4 marbles removed, the water level drops from 80 to 40. So drop in water level for 4 marbles = 80-40 = 40ml

For each marble then, water level drop = 40/4 = 10ml. This is the value of d

Plug this value of d into [1] to get the original water level y₀

80 = y₀ - 2( 10)

80 = y₀ - 20

100 = y₀

or,

y₀ = 100

So original water level is 100ml and the equation for water level after x marbles are removed is

y = 100 - 10x