Find the mistake in the below maths equations

A = 2
A(A-1) = 2(A-1)
A2-A = 2A-2
A2-2A = A-2
A(A-2) = A-2
A = 1

John drives to his office at 20km/hr. After reaching the office, he realizes that today is a holiday. He went back at an average speed of 30km/hr. Discounting the time spent in the stoppage what was the average speed of his journey?

A man dies of old age on his 25 birthday. How is this possible?

What has many teeth, but cannot bite?

Next Number in the Series,

5, 16, 49, 104, ?

What does it mean?

What is the largest amount of money that you can possess in change and still if someone asks you for a dollar, you won't be able to give?

On one occasion, A Boy collects 71 rupees in form of 20 paise and 25 paise. He collects a total of 324 coins.

Can you tell me how many 20-paisa and 25-paisa he got?

What is the word or phrase?

You and your two friends are working in a multinational company. How can you three find out the average salary of you all without disclosing your own salary to the other two?