On a multiple-choice test, Abby randomly guesses on all seven questions. Each question has four choices. Find the probability, to the nearest thousandth, that Abby gets exactly three questions right.
+128408 She wants to answer any 3 of 7 questions correctly...... = C(7,3)
Each question has 25% probability of being answered correctly and a 75% probability of an incorrect answer.....so......we have.....
C(7,3) * (.25)^3 * (.75)^4 = about .173 = about 17.3% chance of answering any three correctly
