Question

A 40 L solution has salt and water in 3:5 ratio. How much water should be added to make ratio 3:7?

• A. 10 L
• B. 12 L
• C. 14 L
• D. 16 L

Answer 1

Answer:

A. 10 L

Total solution = 40 L
Ratio salt : water = 3 : 5

Find initial quantities

Total parts = 3 + 5 = 8

• Salt = ( \frac{3}{8} \times 40 = 15 ) L

• Water = ( \frac{5}{8} \times 40 = 25 ) L

  Let x litres of water be added

New water = ( 25 + x )
Salt remains = 15

New ratio = 3 : 7

So,

$\frac{15}{25 + x} = \frac{3}{7}$

Step 3: Solve

$15 \times 7 = 3(25 + x)$
$105 = 75 + 3x$
$30 = 3x$
$x = 10$

Final Answer: 10 litres of water