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 on 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.

What is the HCF of 36, 72 and 126?

A sphere of radius 5 cm is melted to form a cone with base of same radius. The height (in cm) of the cone is

If x + y = 3, then what is the value of x3 + y3 + 9xy?

If (1 -­ cosA)/(1 + cosA) = x, then the value of x is

What is the value 32cos 39sin 51-sin239 + sin251

If secA = x, then the value of x is

Pipe A can empty a filled tank in 28 hours while Pipe B can fill the same tank, when empty in 35 hrs. If alternatively Pipes A and B are turned on for an hour each time, starting when the tank is full, how long will it take to empty the tank?