Chemist interview questions shared by candidates
There’s a 60% chance it will rain on Saturday AND Sunday. What is the probability that there will be rain on the weekend.
Take the square root of 0.6 to give the individual probability on Sat or Sun = 0.7746. The chance of it being dry all weekend is therefore one minus this number squared = 0.051, so the chance of rain on the weekend is 95%.
Your answer assumes that the probability of it raining on sat or sunday is identical*. Should be stated in question. Ie if it is more likely to rain on sunday than saturday than it changes probabilities....such as probability is 0.9 it rains on saturday and 0.6667 on sunday.
Let the probability it rains on Saturday be p and the probability that it rains on Sunday be q Probability it rains on Sat AND Sun = p*q = 0.6 Also, we know that there are 4 scenarios Rain on Sat, No Rain on Sun Rain on Sat, Rain on Sun No Rain on Sat, Rain on Sun No Rain on Sat, No Rain on Sun The sum of probabilities of these 4 cases = 1 Therefore p*(1-q) + p*q + (1-p)*q + (1-p)*(1-q) = 1 p - p*q + p*q + q - p*q + 1 - p - q + p*q = 1