MAT Exam 2020 Paper

Concept:A four-ring lock allows each ring to show any digit from $0$ to $9$.So repeated digits are allowed while forming the code.Explanation:For each ring, there are $10$ choices.Total possible codes $= 10 \times 10 \times 10 \times 10 = 10^{4}$.In the worst case, the correct code is the last one you try.Therefore, the maximum attempts before getting the right number is one less than the total codes.Maximum attempts $= 10^{4} - 1$.Answer:Option C: $10^{4}-1$.