A glass is filled with liquid, 3 parts of which are water and 5 parts syrup. How much of the mixture must be drawn off and replaced with water so that the mixture may be half water and half syrup?
A glass is filled with liquid, 3 parts of which are water and 5 parts syrup. How much of the mixture must be drawn off and replaced with water so that the mixture may be half water and half syrup? Correct Answer 1/5
Given:
The ratio of water and syrup = 3 ∶ 5
After replacement the ratio of water and syrup = 1 ∶ 1
Concept used:
Always divide the mixture according to the initial ratio
Calculations:
Let the glass initially contain 8 litres of liquid.
Let y litres of this liquid must be replaced with water.
The quantity of water drawn off = 3y/8
Remaining water = 3 – 3y/8
Total water after replacement = 3 – 3y/8 + y
The quantity of syrup drawn off = 5y/8
Remaining syrup = 5 – 5y/8
According to the questions
3 – 3y/8 + y = 5 – 5y/8
⇒ 3 + 5y/8 = 5 – 5y/8
⇒ 10y/8 = 2
⇒ y = 8/5
Part of mixture replaced = (1/8 of 8/5) = (1/5)th part
∴ (1/5)th part of mixture must be drawn off