Answers to the question on houses with dogs and cats

 

There are 20 houses on the 13th Street in a small town. 15 of these houses have a dog. 9 houses have a cat. No house is without a pet. How many houses have a dog and no cat? 

Houses that have a dog = 15

Houses that havea cat =      9

Total number of houses = 20

How can the first two numbers add up to more than the number of houses? That is because some houses have a cat as well as a dog. Consider 15 + 9 - 20 = 4. So, four houses have dogs as well as cats. 

How many houses have a dog and no cat? 15 - 4 = 11 

Srinivasan Ramani 




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