###Human: Bill thought he bought 70 chihuahuas, but some of them turned out to be rats. If the number of rats was 6 times the number of chihuahuas, how many rats did he buy?, ### Assistant: Let r be the number of rats and c be the number of real chihuahuas. We know that r + c = 70 and r = 6c. Substituting the second equation into the first equation, we get 6c + c = 70.
Combining like terms, we get 7c = 70
Dividing both sides by 7, we get c = 10
Substituting this back into r = 6c, we get r = 10 * 6 = 60 
 So the answer is :  60