What is black when you buy it, red when you use it, and gray when you throw it away?

What is the next number in the series?

15 29 56 108 208 ?

Can you find out which triangle will have a bigger area among the following?
1. A triangle with sides 300, 400 and 500
2. A triangle with sides 300, 400 and 700

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

What are the 50th, 63rd and 100th numbers in the sequence below?
4, 5, 8, 8, 9, 9, 12, 13, 13, 13, 17, 18, ...

Can you find the missing letter in the sequence?
S - T - I - L - ? - T - F - Y - C

Identify The phrase in the picture.

What begins with T, ends with T, and has T in it?

I have 50 feet long of cloth, I need to create 50 handkerchiefs each size of 1 foot. I take one minute to cut a 1-foot handkerchief. So how long will it take to cut 50 handkerchiefs?

They came out at night, without being called.
They lost at day, without being stolen.
Who are they?