GATE Computer Science (CS) 2015 Shift 2 Solved Paper

Let 𝑋 and 𝑌 denote the sets containing 2 and 20 distinct objects respectively and 𝐹 denote the set of all possible functions defined from 𝑋 to 𝑌. Let 𝑓 be randomly chosen from 𝐹. The probability of 𝑓 being one - to - one is ________.