B, in order to add or subtract fractions, we must have a common denominator. Since 15 and 2 are not the same, we must find the least common multiple, or LCM, of 2 and 15.
Let's list multiples of 15. We have 15, 30, 45, 60, ...
Now, we can see that 30 is already divisible by 2, right? So is 60, but we are looking for the LEAST common multiple.
So, our common denominator is going to be 30.
Let's start with 9/15. What do we have to multiply 15 by to get to 30? 2. We have to multiply the numerator, 9, by 2 to get a new numerator. We end up with 18/30.
Now, let's do 1/2. We have to multiply 2 by 15 to get 30, and we have to do the same thing to the numerator. 1 x 15 = 15, so our new fraction is 15/30.
Now, we have 18/30 - 15/30. All we do now is subtract the numerators and the denominator stays the same. Our difference is 3/30.
Now, are 3 and 30 both divisible by anything? 3, right? How many 3's make 3? 1.
How many 3's make 30? 10.
So, our reduced answer is 1/10.
I hope this makes sense!
