In a Question paper there are 4 multiple choice questions.

BTGModeratorVI wrote: ↑

Mon Apr 13, 2020 3:36 pm

In a Question paper there are 4 multiple choice questions. Each question has 5 choices with only one choice as the correct answer. What is the total number of ways in which a candidate will not get all the four answers correct?

A. 19
B. 85
C. 120
D. 624
E. 1024

Answer: D
Source: Princeton Review

We can use the following equation:

Total number of ways to answer all questions - number of ways to get all questions correct = the total number of ways in which a candidate will not get all four answers correct

5 x 5 x 5 x 5 - 1 x 1 x 1 x 1 = 625 - 1 = 624

Answer: D

BTGModeratorVI wrote: ↑

Mon Apr 13, 2020 3:36 pm

In a Question paper there are 4 multiple choice questions. Each question has 5 choices with only one choice as the correct answer. What is the total number of ways in which a candidate will not get all the four answers correct?

A. 19
B. 85
C. 120
D. 624
E. 1024

Answer: D
Source: Princeton Review

Let's first determine the TOTAL number of ways the test can be completed.
The 1st question can be answered in 5 different ways (A, B, C, D, or E).
The 2nd question can be answered in 5 different ways (A, B, C, D, or E).
The 3rd question can be answered in 5 different ways (A, B, C, D, or E).
The 4th question can be answered in 5 different ways (A, B, C, D, or E).

By the Fundamental Counting Principle (FCP), the total number of ways we can complete test = (5)(5)(5)(5) = 625 ways

So, there 625 possible outcomes
Among those 625 possible outcomes, ONLY 1 outcome is such that all four questions ARE answered correctly.
This means, in the remaining 624 outcomes, the four questions are NOT all answered correctly.

Answer: D

Cheers,
Brent