Question 1033544
p=0.2; q, or 1-p=0.8
exactly 7 questions right
10C7(0.2)^7(0.8)^3.
The 10C7 is the number of ways 7 questions can be answered correctly out of 10.  It is 10!/7!3!=120
120*0.2^7*0.8^3=0.0008
For any number of questions right, use 0.2, which is the likelihood of guessing right with 5 choices, 1/5, and raise it to the number you want.  Then use the complement of 0.2, or 0.8, and raise it to the number you want.  The exponents must add up to the number of trials, in this instance 10.