If 80 litres of milk solution has 60% milk in it, then how much milk should be added to make milk 80% in the solution?

Costs of two articles were in the ratio of 16: 23. The cost of first articles increases by 10% and that of second by Rs.477. Now the costs of two articles are in a ratio of 11: 20. The price of the second article (in Rs.) in the beginning was-

There are three bottles of mixture of syrup and water of ratio 2 : 3,  3 : 4,  7 : 5. 10 Litres of first and 21 Litres of second bottles are taken. How much quantity from third bottles is to be taken so that final mixture from three bottles will be of ratios 1 : 1. 

The ratio of the age of a son and father is 1: 4. After 9 years, the ratio will be 2: 5. What is the present age (in years) of the son?

There are three containers of equal capacity. The ratio of Sulphuric acid to water in the first container is 3 : 2, that in the second container is 7 : 3 and in the third container it is 11 : 4 . If all the liquids are mixed together, then the ratio of Sulphuric acid to water in the mixture will be: 

Find the area of the shaded region if the radius of each of the circle is 1 cm.

Two trains starts from place A and B, 450 km apart towards each other. Both trains start simultaneously. A crow sitting on one train start flying at the same time towards the other train and as soon as it reaches the second train, it flies back to the first train and it continues in this manner flying backward and forwards from one train to the other until the train meet. Both train travel  at a speed of 45 km / h and the crow flies at 100 km / h total distance covered by the crow will be