If 21x = 79x, what is the value of x?

What's the next in the series?

H, Be, F, S, Mn, Kr, In, Gd, Tl, ?

Find the next number in the sequence

1, 2, 6, 21, 88, __?

A patient was diagnosed with some ailment. He was given five different tablets to take at night at an interval of 15 minutes.

How long will it take the patient to consume all the five tablets?

A man hijacks an aeroplane transporting both passengers(8 of them) and valuable cargo. After taking the cargo, the man demands nine parachutes, puts one of them on, and jumps, leaving the other eight behind. Why did he want eight?

John is asked to stand behind Jacob and Jacob is asked to stand behind John. Both of them feel confused about it and don't know what to do?

But it is quite possible, do you know how?

At my favorite fruit stand,
an orange costs 18,
a pineapple costs 27,
and a grape costs 15.
Using the same logic, can you tell how much a mango costs?

I add 5 to 9 and get 2. The answer is correct, so what am I?

What do you answer even though it never asks you questions?

Can you write down eight eights so that they add up to one thousand?