What common phrase is represented by the below lines

Easy going:
Weak, 'I'm going.'
Tough, 'I'm staying.'

Medium going:
Weak, 'I'm going.'
Tough, 'I'm staying.'

Tough going:
Weak, 'I can't do it, I'm staying!'
Tough, 'Let's get going.'

When it is alive we sing, when it is dead we clap our hands. What is it?

What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?

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

If nine thousand, nine hundred nine dollars is written as $9,909,
how should twelve thousand, twelve hundred twelve dollars be written?

There was an aeroplane crash, every single person died, but two people survived. How is this possible?

What is the centre of gravity?

In a competitive exam, each correct answer could win you 10 points and each wrong answer could lose you 5 points. You sat in the exam and answered all the 20 questions, which were given in the exam.
When you checked the result, you scored 125 marks on the test.

Can you calculate how many answers given by you were wrong?

Which digit occurred maximum times between the number 1 and 1000?

Can you replace the X (both small and big x) with the numbers between 1 to 19 such that all the rows of 3 numbers between X (big x) sum to 23?