Coding and Decoding questions for UPSC Prelims

In some code, letters P, Q, R, S, T represent numbers 4, 5, 10, 12, 15. It is not known which letter represents which number. If Q – S = 2S and T = R + S + 3, then what is the value of P + R – T?

If in a certain code, ‘POT’ is written as ATOP and ‘TRAP’ is written as APART, then how is ‘ARENA’ written in that code?

In the expression 5 * 4 * 3 * 2 * 1, * is chosen from, +, –, × each at most two times. What is the smallest non negative value of the expression?

If 7 ⊕ 9 ⊕ 10 = 8, 9 ⊕ 11 ⊕ 30 = 5, 11 ⊕ 17 ⊕ 21 = 13, what is the value of 23 ⊕ 4 ⊕ 15?

If the order of the letters in the English alphabet is reversed and each letter represents the letter whose position it occupies, then which one of the following represents ‘LUCKNOW’?

In a code language ‘MATHEMATICS’ is written as ‘LBSIDNZUHDR’. How is CHEMISTRY’ written in that code language?

The letters from A to Z are numbered from 1 to 26, respectively. If GHI = 1578 and DEF = 912, then what is ABC equal to?

If ‘$’ means ‘divided by’; ‘@’ means ‘multiplied by’; ‘#’ means ‘minus’, then the value of 10#5@1$5 is