In the original mixture, ratio of water to oil
= 90 : 10
= 9 : 1


In the new mixture ,

100% - 96% = 4%

4% of the new mixture is oil.

Ratio of water to oil

= 96 : 4
= 24 : 1



Concept: one item unchanged

The amount of oil was unchanged. So we should make the units the same for both ratios for the oil.

But luckily, they are both at 1 unit so no need to change. The ratios are directly comparable.


So there were 9 units of water at first.
After adding 105ml of water, it increased to 24 units.

24 units - 9 units = 15 units

So 15 units of water were added.

15 units = 105ml
1 unit = 105ml ÷ 15 = 7ml

This is the amount of oil in the glass (1 unit = 7ml)

100% - 68% = 32%

Number of men wearing glasses = 32% of people wearing glasses
= 40% of all the men
= 40% of all the women

(Since there are equal numbers of men and women. This does not mean 40% of all the women wear glasses. It is just the same number as 40% of the women)

Divide both sides by 8,

4% of people wearing glasses = 5% of women

Multiply by 17 ,

68% of people wearing glasses = 85% of women


% of women who do not wear glasses
= 100% - 85%
= 15%

Alternatively, use ratio.

Concept : total unchanged


Women (wear glasses) : Women (don't wear glasses : Total Women

= 40 : 60 : 100

Men (wear glasses) : Men (don't wear glasses

= 40 : 60 : 100


Men (wear glasses) : Women (wear glasses)

= 32 : 68
= 8 : 17 (after dividing by 4)


Make the units for men who wear glasses the same for the ratios, multiply by 5.

Men (wear glasses) : Women (wear glasses)

= 8 : 17
= 40 : 85



So 85% of women wear glasses, which means 15% don't.

Thank you for helping