Bob had 18 crackers sam eat 1/6 of the crackers and sue ate 1/3 of the crackers. how many crackers did bob have left

We can add 1/6 & 1/3 together to find out the total amount of crackers that were eaten:

1/6 + 1/3   (Find the Common Denominator. In this case it is 6.) 
= 1/6 + 2/6
= 3/6 (Now find the Lowest Terms. Both 6 & 3 divide into 3)
= 1/2 (In Lowest Terms)

This means that 1/2 of the Crackers have been eaten.

1/2 of 18 = 9 

Therefore, Bob has 9 Crackers left. 

The first thing to do is make both fractions over 6: 
1/3 = 2/6
Sue at 2/6 of the crackers. 

Now we can add the fractions: 
2/6 + 1/6 = 3/6

The next thing to do is cancel down the fraction. 
3/3 = 1
6/3 = 2
3/6 = 1/2

Now that we know that half of the crackers have been eaten, we halve the total amount: 
18 X 1/2 = 18 / 2 = 9

Bob had 9 crackers left.