What is common among 11, 69, and 88?

How can you make the following equation true by drawing only one straight line: 5+5+5=550 ?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

What's the next in the series?

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

There are two words one resembles the "state of rest" and the other is related to "writing/reading material".

Can you name these two words which also sound similar?

A mile-long train is moving at sixty miles an hour when it reaches a mile-long tunnel. How long does it take the entire train to pass through the tunnel?

Can you solve below mathematical equation?

2^1234 - 2^1233

Can you replace the question mark with the correct letter?

6 + 6 + 6 = N
7 + 7 + 7 = E
8 + 8 + 8 = R
0 + 0 + 0 = ?

You can hear me, but you can't touch or see me.

What am I?

If it took eight men ten hours to build a wall, how long would it take four men to build it?