We know that factors are numbers we can multiply together to get another number.

So 1 and 15 are factors of 15.
Also, 
So 3 and 5 are factors of 15.
We have got 1, 3, 5, 15 all are factors of 15.
Multiple is a number that can be divided by another number without a remainder.
So we know that 3 is a multiple of 3, as
and also 15 is a multiple of 3, as
.
But 1 and 5 are not multiples of 3.
We have got the required answer.
1 and 5 are factors of 15 but not multiples of 3.