using four eights (8) and a one (1) and one mathematical symbol , create the number 100

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

What Word am I Looking For ?

Which tank will fill first?

To attend world science seminar, A famous chemist from Mexico visit
London. In the lab, the scientist was killed and his six assistants were under suspicion of killing the chemist.
Name of six assistants: Austin, Wayne, Dege, Oscaru, Lingard, and Rojo.
He left a note "76-20-44 79-16-22-7"

A local detective Jack was called to solve the case,

After reading the note, Jack instantly asked the police to arrest the murderers.

Who are the murderers?

One is to three as three is to five and five is to four and four is the magic number.
What is the pattern?

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

O T T F F S S ?

You need to move three matchsticks to form three squares. Can you do it?

Can you identify the direction in which this bus is moving; left or right?

Hint: The bus is moving on the roads of London.

How will you measure 15 minutes using two hourglasses of 7 minutes and 11 minutes respectively?

You have three orange, two pink and five purple balls in the drawer beside your bed. There is no electricity and the room is entirely dark. How many balls must you take out to ensure at least one ball of each colour at least?