谢谢.got all the question wrong: (3/4)^5
got one question right: (1/4)*(3/4)^4*5
got two questions right: (1/4)^2*(3/4)^3*10
got three questions right: (1/4)^3*(3/4)^2*10
got four questions right: (1/4)^4*(3/4)*5
got all questions right: (1/4)^5
add all the possibilities together equals to 1.
got all the question wrong: (3/4)^5
got one question right: (1/4)*(3/4)^4*5
got two questions right: (1/4)^2*(3/4)^3*10
got three questions right: (1/4)^3*(3/4)^2*10
got four questions right: (1/4)^4*(3/4)*5
got all questions right: (1/4)^5
add all the possibilities together equals to 1.