If eleven plus two equals one, what does nine plus five equal?

Transform the word THINK into BRAIN while changing only one letter at a time in a manner that each of the word in the process is a real word!!!

There is a five-letter word which has 3 consonants(all are same) and 2 different vowels.
Also, something wrong is associated with the word.

Can you name it?

If you remove one from eleven, it becomes ten. If you remove one from nine, it becomes ten.

How is this possible?

How many times can you subtract the number two from the number fifty?

You are provided with a grid (as shown in the picture). Can you fill the squares with numbers 1-8 in a manner that none of the two consecutive numbers are placed next to each other in any direction (vertically, horizontally or diagonally?)

I am Huge on Sunday and Saturday.
I am small from Tuesday to Thursday.
I do not exist on Monday and Friday.
Who am I?

There is a barrel with no lid and some wine in it. 'This barrel of wine is more than half full,' said Curly. 'No it's not,' says Mo. 'It's less than half full.' Without any measuring implements and without removing any wine from the barrel, how can they easily determine who is correct?

A shepherd had 18 sheep, out of which, all but ten died.

Can you tell us how many sheep was he left with?

A father's child, a mother's child, yet no one's son.

Who am I?