Find the number of sides of a regular polygon whose interior angle is twice the exterior angle.

Thirty boys and x girls sat for a test. The mean of the boys' and girls' scores were 6 and 8 respectively. Find x if the total score was 468.

A man bought a second hand photocopying machine for ₦34,000. He serviced it at a cost of ₦2,000 and then sold it at a profit of 15%. What is the selling price?

A student measures a piece of rope and found that it was 1.26m long. If the actual length of the rope was 1.25m, what was the percentage error in the measurement.