Question

In a class consisting of 40 boys and 30 girls, 30% of the boys and 40% of the girls are good at Mathematics. If a student selected at random from that class is found to be a girl, then the probability that she is not good at Mathematics is:

• A. \( \frac{3}{5} \)
• B. \( \frac{2}{5} \)
• C. \( \frac{3}{10} \)
• D. \( \frac{7}{10} \)

Hint:

To calculate the probability that a student is not good at Mathematics, subtract the number of students good at Mathematics from the total number of students in the given group, and then divide by the total number of students in that group.

Answer 1

The Correct Option is A

We are given that in a class consisting of 40 boys and 30 girls:
- 30% of the boys are good at Mathematics.
- 40% of the girls are good at Mathematics.
The total number of boys is 40, and the total number of girls is 30. We are asked to find the probability that a randomly selected girl from the class is not good at Mathematics.
Step 1: The number of girls who are good at Mathematics is: \[ \text{Good girls} = 40\% \times 30 = \frac{40}{100} \times 30 = 12 \] Thus, the number of girls who are not good at Mathematics is: \[ \text{Not good girls} = 30 - 12 = 18 \] Step 2: The total number of girls in the class is 30. Therefore, the probability that a randomly selected girl is not good at Mathematics is: \[ P(\text{Not good at Mathematics | Girl}) = \frac{\text{Not good girls}}{\text{Total girls}} = \frac{18}{30} = \frac{3}{5} \] Thus, the probability that the selected girl is not good at Mathematics is \( \frac{3}{5} \).