By removing one matchstick and adding one matchstick, can you convert the word "ZOO" to an animal name?

Look at the below sequence of letters and tell us what the next letter should be:

O T T F F S S ?

A boy collects white seashells from the sea and brings them home every night. When he has enough of them, he decides to sell them to a trader.

The trader is ready to buy the shells and he asks the boy about the quantity. At this, the boy starts calculating. He has a giant box that contains 3 mini boxes. Two of them have another mini box inside. If the giant box can hold 50 shells, how many brown shells can he sell to the trader?

A red house is made out of red bricks. A yellow house is made out of yellow bricks. And, a blue house is made out of blue bricks. So, what is a greenhouse made of?

What does this rebus riddle means ?

If all Goats are Sheep and all Sheep are Deers, are all Deers Goats ?

What time is it when an elephant sits on a fence?

John is selling fruits.
He sells grapes at $30, Dates $25, and a Wolfberry $45.
At what price does he sell fig?

PS: Logical Thinking

A man dies of old age on his 25 birthday. How is this possible?

Can you replace the question mark with the correct number?