My best answer is that the probability is 35/100 that the student chosen at random owns neither a laptop nor a mobile phone.
Step-by-step explanation:
If you go back and read the introductory passage, you will notice it says, "In a group of 100 students... 35 own either a laptop or a mobile phone, but not both." And I think the other numbers, I.E. 25 and 40, were just meant to throw us off. Therefore, I think 35/100 is the probability.
There are 4 positions on the board. There are 15 possible candidates for the first position. That leaves 14 candidates for the second position. Which leaves 13 for the third position, and 12 for the fourth position.
