A standard fair six-sided die is rolled once. What is the probability of rolling a prime number?
Answer and explanation
Correct answer: B. 1/2
- Step 1: Sample space: S = {1, 2, 3, 4, 5, 6}, so n(S) = 6. Prime outcomes are {2, 3, 5}, so n(E) = 3. Step 2. Probability = n(E) / n(S) = 3 / 6 = 1/2. Answer: 1/2. Why not the others: 1/3 counts only two primes; 2/3 erroneously includes 1 as prime; 1/6 is probability of rolling a single specific number.
Practise more Geometry, Mensuration and Mental Ability.
Free questions with an explanation for every one, and full timed Bangladesh Civil Service Preliminary Examination mock tests.
More Geometry, Mensuration and Mental Ability questions
- Two angles are complementary, and their degree measures are in the ratio 2 : 3. What is the degree measure of the larger angle?
- An angle measures such that its supplementary angle is four times its complementary angle. What is the measure of this angle in degrees?
- The three interior angles of a triangle are in the ratio 3 : 4 : 5. What is the degree measure of the largest interior angle?
- What is the degree measure of each exterior angle of a regular octagon (an 8-sided regular polygon)?
- What is the sum of all interior angles of a convex hexagon (a 6-sided polygon)?
- A right-angled triangle has perpendicular legs measuring 9 cm and 12 cm. What is the length of its hypotenuse?