Evaluate the following.

sin 25° sin 65° – cos 25° cos 65°.

A man buys a machine for Rs.5,000. After one year, he sells it for Rs.6000. After two years, again he buys the same machine at Rs.8,000 and sells it for Rs.10,000. Find his overall profit percentage for both the transactions.

The product of the two numbers is 1500 and their HCF is 10. The number of such possible pairs is/are: 

Find the value of the given expression.

 $$\sqrt { 8+\sqrt { 1681} \ } \ $$

If radius of a sphere is decreased by 48%, then by what percent does its surface area decrease?

The ratio of the incomes of two employees is 7 : 4, and the ratio of their expenditures is 3 : 1. If each of them manages to save ₹4,800 per month, find the sum of their monthly incomes (in ₹). 

Find the value of given expression.

30 – [40 – {56 – (25 – 13 – 12)}]

What is the volume of the largest sphere that can be carved out of a wooden cube of side 21 cm?$$( π{22\over 7})$$