I am looking for a word that change both gender and number when i add the letter 'S'.

What Word am I Looking For ?

What word begins and ends with an E, but has only one letter?

A man has a barrel filled with oil that weighs 100 pounds, and then he puts something into it. Now the barrel weighs less than 100 pounds. What did he put in the barrel?

Which statement is true out of the following?
One statement here is false.
Two statements here are false.
Three statements here are false.

When I get multiplied by any number, the sum of the figures in the product is always me. What am I?

A Scientist was fifty years old in the year 2000 but he was forty years old in the year 2010. How can this be possible?

PS: It has a logical answer.

John was running from 40 thieves. John has got 3 gold boxes which weigh as 4kg, 2kg, and 1kg respectively. A witty man asked John to stay with him for seven days in exchange for 1kg gold per day. John needs to stay there for seven days and also do not want to give the witty man any advance. How can John pay for his seven days stay?

What comes
Once in a Year
Twice in a Month
4 times in a Week
6 times in a Day

Its something that each of us devours,
Not just us but birds, beats, trees, and flowers,
Frets iron and nibbles steel,
Toil hard stones to meal,
Exterminates king, collapse town,
And blows the mountains down.

What does this below rebus puzzle mean?