Question

in a multiple choice test there are 5 possible answers to each 20 questions.if a candidate guess the answer each the mean no. of correct answer

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Answer 1

As others have pointed, the probability is (1/5)^20, or 1 in 95,367,431,640,625, or roughly 1 in 100 trillion (10^14, or 1 followed by 14 zeros).

To give some perspective into this huge number, here are two comparisons:

- it's about a million times less likely than winning on a lottery where you have to get 6 numbers right out of 60 possible choices

- it's about 100 times less likely than correctly predicting, at random, whether the stock market will go up or down in each of the following 40 years

Better to start studying for the test...