Question: 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? Think carefully first, then make a decision:
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.