Mary travels to work by train every day: The probability that her train will be late on any day is 0.15 - Edexcel - GCSE Maths - Question 11 - 2019 - Paper 2

To find the probability that her train will be late on at least one of the two days, we can use the complementary probability:

1. First, calculate the probability that her train is not late on both days:

   • Probability of not being late on Thursday: 0.85
   • Probability of not being late on Friday: 0.85

2. Therefore, the combined probability of not being late on either day: $P( ext{not late both days}) = 0.85 imes 0.85 = 0.7225$

3. Now, we subtract this from 1 to find the probability of being late on at least one day: $P( ext{late at least one day}) = 1 - P( ext{not late both days}) = 1 - 0.7225 = 0.2775$

Thus, the probability that her train will be late on at least one of these two days is 0.2775.