The ratio of milk and water in a mixture is 4 : 3. If we add 2 litres of water, the ratio of milk and water becomes 8 : 7. What is the quantity of the final mixture?

Initially mixture  is 4:3 

After adding 2 lit water it becomes 8:7.....(1)

It means quantity of milk is remain unchanged and water is changed in mixture 

4:3 $$\times 2$$ (to equal the milk quantity )

= 8:6 .......(2)

Now milk ratio is same and water is changed after adding water

so difference in the ratio (8:7)-(8:6) = 0:1

1unit -> 2lit 

Given that final mix. Ratio =8:7

 Milk =$$ 8\times 2$$= 16 litre

Water = $$ 7\times 2$$= 14 litre

Total= 16+14=30 litre