Quantitative Aptitude - Arithmetic Ability Questions

In the following question, four number pairs are given. The number on left side of (–) is related to the number of the right side of (–) with some Logic/Rule/Relation. Three are similar on basis of same Logic/Rule/Relation. Select the odd one out from the given alternatives.

The value of a machine depreciates at the rate of 20% per annum. If its present value is Rs 96000, then what was the value (in Rs) of the machine 2 years ago?

When [x + (1/x)] = 5, then what is the value of [x – (1/x)]?

What is the digit in unit's place of the product 51 x 52 x 53 ...... 59?

If 5x - (1/2)(2x -7) = 5.5, then what is the value of x?

What is the value of S = 11x3x5 + 11x4 + 13x5x7 + 14x7 + 15x7x9 + 17x10 + ... upto 20 terms. Then what is the value of S? 

What is the equation of the line which passes through the points (3,­2) and (5,3)?

What is the value of equation a3+b3+c3-3abc if a2+b2+c2=ab+bc+ca+4 and a+b+c = 4.