One of the numbers are negative
Remember this... a negative divided by a positive will result in a negative and a negative divided by a negative will result in a positive, the same goes for multiplication
Essentially, the rule goes as so: odd + odd = even, even + even = even.
Although that may not be the answer you're looking for, it is a math rule that is never debunked and essentially the premises for why you get an even sum practically always depending on the numbers.
Hope this helps!
Answer:

And we can find this probability to find the answer:

And using the normal standar table or excel we got:

Step-by-step explanation:
Let X the random variable that represent the amounts of nocatine of a population, and for this case we know the distribution for X is given by:
Where
and
We have the following info from a sample of n =37:
the sample mean
And we want to find the following probability:

And we can use the z score formula given by;

And if we find the z score for the value of 0.872 we got:

And we can find this probability to find the answer:

And using the normal standar table or excel we got:

Answer: 5
15/3 = 5
There are 5 doughnuts left.