Ratio and Proportion

If the ratio of boys to girls in a class is 3:4 and there are 21 boys, how many girls are there?

A recipe uses 2 cups of sugar for every 5 cups of flour. How much sugar is needed for 20 cups of flour?

The ratio of the ages of Amit and Rahul is 5:7. If Rahul is 21 years old, what is Amit's age?

If 3 pencils cost ₹15, how much will 7 pencils cost?

Two numbers are in the ratio 4:9. If their sum is 65, what are the numbers?

In a cricket match, the ratio of runs scored by Player A to Player B is 7:9. If Player B scored 81 runs, what is the total runs scored by both?

The ratio of the length to the breadth of a rectangle is 5:3. If the perimeter is 64 cm, find the length and breadth.

If 5 kg of sugar costs ₹150, what will be the cost of 8 kg of sugar? Also, find the cost per kg.