Step-by-step explanation:
the break down probabilities are for the same given day ? one day ?
if that is so, then the expected value for a break down day for tractor 1 will be 34 days (rounded up 100%/3%), and for tractor 2 20 days (100%/5%).
that would be horrible. a tractor would only work for about a month without major repair.
because normally such probabilities are given for a warranty period like 1 or 3 or 5 years.
but the description does not say anything about that. so, we have to go with the primary assumption.
so, the question is about the probability that both things happen at the same time (the same day).
this is like asking for the probability of rolling a double 6 with two dice - both events (a 6 on a die) have to happen "together". so it is the probability of one event multiplied by the probability of the second event : 1/6 × 1/6 = 1/36
5% = 0.05 (5% is 5 hundredths) = 5/100
3% = 0.03 (3% is 3 hundredths) = 3/100
now both events (break-down of both tractors) happen together means 5/100 × 3/100 = 15/10000 = 0.0015
that means the probability in % is 0.15%
that means in other words, this event (both tractors breaking down on the save day) is expected to happen 15 times in 10000 days, or once every 667 days (or roughly every 2 years).
