Q1. What should come in place of the question mark (?) in the following alpha-number series? X4Z, T9U, P25P, L49K, ?, D169A
A G121G
B H121F Correct
C G81F
D H81F
Explanation
The first letters move four places backward each time: X, T, P, L, H, D. The middle numbers are squares of consecutive prime numbers: 2 squared gives 4, then 3 squared gives 9, 5 squared gives 25, 7 squared gives 49, 11 squared gives 121 and 13 squared gives 169. The last letters move five places backward: Z, U, P, K, F, A. Therefore the missing term is H121F. G121G, G81F and H81F break either the letter movement or the square-number pattern.