Solid metallic spheres of diameters 12 cm, 16 cm and 20 cm respectively, are melted to form a single solid sphere. Find the radius of the resulting sphere.

A man deposits ₹ 1800 per month in a recurring deposit account for 2 years. If he gets ₹ 3600 as interest at the time of maturity, find the rate of interest.

The mean of 6 different data is 12. If 5 of these data are 16, 18, 12, 13 and 8; the sixth data is :

1. 63

2. 6 × 12

3. 5

4. 12 × 3