Three of the following four letter-clusters are alike in a certain way and one is different. Pick the odd one out.

Select the set in which the numbers are related in the same way as are the numbers of the given sets.

(NOTE : Operations should be performed on the whole numbers, without breaking down the numbers into its constituent digits. E.g. 13 – Operations on 13 such as adding /subtracting /multiplying etc. to 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)

(12, 8, 20)

(7, 3, 15)

The second number in the given number pairs is obtained by performing certain mathematical operation(s) on the first number. The same operation(s) are followed in all the number pairs, EXCEPT one. Find that odd number pair.

Which two signs should be interchanged to make the given equation correct?

312 – 13 × 14 + 207 ÷ 4 = 539