What does this rebus riddle means ?

Take away the whole and some still remain. What is it?

Manish has to secure 40% marks to pass his B.tech final exams.
He got just 40 marks and failed by 40-marks.

What is the maximum marks?

I am sure no one can have two things for dinner. what are they?

Count the number of times the letter "F" appears in the following paragraph:

FAY FRIED FIFTY POUNDS OF
SALTED FISH AND THREE POUNDS
OF DRY FENNEL FOR DINNER FOR
FORTY MEMBERS OF HER FATHER'S FAMILY.

If "P" means "-", "Q" means "/", "R" means "+", and "S" means "*" then find the value of the following:

21 Q 7 R 9 S 10 P 13

I have branches, but no fruit, trunk or leaves. What am I?

Quickly Solve this riddle

7 - 4 + 3 * 0 + 1 = ?

Here is a mathematical expression that also secretly tells a movie name. What movie is that?

Can you name some countries which do not have the alphabet 'A' in them?