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?

2 Answers
Nov 10, 2016

250 ml


2 litres = 2000 ml

#2000/8 = 250#

Nov 13, 2016

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


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