Problem number 12. There are 7 houses north of road A, 8 houses east of road B, and 5 houses south of road A. How many houses are west of road B? Here is a picture showing road A and road B. Let's ignore road B for now and think about road A. Looking just at road A, we know that there are 7 houses north of it and 5 houses south of it. Now since we are ignoring road B, it doesn't matter which of these houses are on the west side or on the east side. In fact, this will be all the houses because a house has to either be north of road A or south of road A in this problem. So we know that there is a total of 7 plus 5 or 12 houses on this map. Now we can figure out how many are west of road B. Since there are 8 houses east of road B, the remaining houses will be west of road B. 12 minus 8 is 4. So there are 4 houses west of road B. The answer is A.

houses

road A

road B

north

west