Question

There are 15 pens and 10 pencils in a box. One object is selected at random and then replaced. Another is the selected. Find the probability that:

1. The first object selected is a pen and the second is a pencil
2. One is a pen and the other is a pencil
3. Both are pencils
4. At least one is a pen

Four questions in total

Answer 1

Explanation:

1. P(pen then pencil) = 15/25 × 10/25 = 3/5 × 2/5 = 6/25

2. P(pen then pencil) + P(pencil then pen) = 6/25 + 6/25 = 12/25

3. P(pencil then pencil) = 10/25 × 10/25 = 2/5 × 2/5 = 4/25

4. P(at least 1 pen) = 1 − P(no pen) = 1 − 4/25 = 21/25