Find the Next Number in the Sequence

2 9 3 1 8 4 3 6 5 7 ?

In a competitive exam, each correct answer could win you 10 points and each wrong answer could lose you 5 points. You sat in the exam and answered all the 20 questions, which were given in the exam.
When you checked the result, you scored 125 marks on the test.

Can you calculate how many answers given by you were wrong?

Can you count the number of triangles in the given picture?

If,
9 * 8 * 7 = 65
8 * 7 * 6 = 50
7 * 6 * 5 = 37

Find
6 * 5 * 4 = ?

During which month do people sleep the least?

A maths symbol is hidden in the below Bar Graph. Can you decipher it?

What is at the end of a rainbow?

What's the next in the series?

H, Be, F, S, Mn, Kr, In, Gd, Tl, ?

What can run but never walk, have a mouth that never speaks, have a head that never weeps, and have a bed but never sleeps?

In Greek mythology, the Sphinx sat outside of Thebes and asked this riddle of all travellers who passed by. If the traveller failed to solve the riddle, then the Sphinx killed him/her. And if the traveller answered the riddle correctly, then the Sphinx would destroy herself. The riddle:

What goes on four legs in the morning, on two legs at noon, and on three legs in the evening?

Oedipus solved the riddle, and the Sphinx destroyed herself.