Amultiple choice test has ten questions each with four possible answers of which only one is the correct answer . what is the probability that sheer guess work yields 5 to 10 correct answers ?

This can be solved by using the binomial distribution, where the probability of guessing the correct answer to a question is 0.25.
P(5 correct) = 0.0584
P(6 correct) = 0.0162
P(7 correct) = 0.0031
P(8 correct) = 0.0004
P(9 correct) = 0.0000
P(10 correct) = 0.0000
P(5 to 10 correct) = 0.0781 or 7.81%

You can find the area of a rectangle by multiplying the length and height. so multiply 1/2*7/4(which is the simpler version of 1 3/4) and you get 7/8 as your answer.