Which one will replace the question mark?

Direction: Select the related word from the given alternatives.

5 : 2431 :: 8 : ?

Direction: In the following, select the related word from the given alternatives.
Heat : Convection :: Space : ?

The sum of the present ages of two cousins is 46 years. Eight year ago, the elder one was twice as old a the younger one. What is the present age of the elder cousin?

In a string of 20 beads, the average weight of the first 14 beads is 25 grams and that of the last 6 beads is 8 grams. What is the average weight of all the beads?

In each of the following questions, four numbers are given out of which three are like in some manner while one is different. Choose the one which is different from the rest three?

Find the odd word from the following:

In the given figure, how many wooden plates are there?