"Two people, both aged 60, start saving money monthly, except the second one doesn't start saving until they are both 65. If the first person is saving $700 a month, and the second $100 a month, how long will it be after the second person starts saving for their accounts to be even (excluding interest, simple or otherwise)?"
I looked at my dad, then got up and asked him for a pen and paper. I clarified the problem, considered a tiny bit more and scribbled this down: 4200+700x=1000x then I looked at what I had written and corrected it to: 42000+700x=1000x and handed it to my dad while asking if that was what he had come up with. He said nothing, but asked me if I was sure. I talked through it with him and he was shocked to find out that x=140, or 11 years 8 months, when the two people are almost 77.
I then walked back here while yelling to my stepmom that: "He tricked me, telling me it was a bookkeeping question when it was an algebra word problem!"