A dice is thrown 80 times. If the probability of having an even number is 7/10 then how many times an odd number appears on dice?

Answer

To solve the problem step by step, we can follow the reasoning presented in the video transcript:

1. **Understanding the Problem**: We know that a dice is thrown 80 times, and the probability of rolling an even number is given as \( \frac{7}{10} \).

2. **Finding the Probability of Odd Numbers**: The total probability of all outcomes must equal 1. Therefore, the probability of rolling an odd number can be calculated as:
\[ P(\text{odd}) = 1 - P(\text{even}) = 1 - \frac{7}{10} \]
\[ P(\text{odd}) = \frac{3}{10} \]

3. **Calculating the Expected Number of Odd Rolls**: To find out how many times an odd number appears when the dice is thrown 80 times, we multiply the total number of throws by the probability of rolling an odd number:
\[ \text{Number of odd rolls} = n \times P(\text{odd}) = 80 \times \frac{3}{10} \]
\[ \text{Number of odd rolls} = 80 \times 0.3 = 24 \]

4. **Conclusion**: Therefore, the number of times an odd number appears on the dice is **24**.