Question

Kamal has to fill the same measuring cup 8 times to get 2 liters of water. How many milliliters of water does the cup hold?

Answer 1

250 ml

Explanation:

2 litres = 2000 ml

`2000/8 = 250`

Answer 2

Further explanation (expansion) on the solution by SS. Showing where his shortcut method comes from.

Explanation:

Although it does not look as though people are using ratio when solving this type of question they are.

Initial condition expressed as a ratio in fraction form gives:

`("2 Litres")/("8 cups")" "` this is stating that for every 8 cups we have 2 litres

The change required is that we have millilitres and 1 cup
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
`color(blue)("Dealing with the millilitres first")`

Known that 1 Litre = 1000 millilitres

So 2 Litres = 2000 millilitres

The actual volume has not changed, just the units of measurement. So we now have:

`("2000 millilitres")/("8 cups")`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
`color(blue)("Dealing with the 8 cups")`

As this is a ratio we need to maintain proportionality.

So if we reduce the count of cups we need to reduce the count of millilitres by an appropriate a mount.

To change 8 cups into 1 cup divide by 8. For multiply or divide in ratios what you do the bottom you do to the top.

Divide top and bottom by 8

`("2000 millilitres")/("8 cups") ->(color(red)("2000 millilitres"-:8))/("8 cups"-:8)`

`" "color(red)(uarr)`

`color(red)("The bit in red is where the shortcut comes from")`

`=(250" millilitres")/(1" cup")`

So 1 cup holds 250 millilitres