Heh. I am unsure why your comment triggered this memory, but here it is:
My wife was worried that she did not have enough gas to get to the gas station. Her car went 300 miles on a tank of gas and she had driven 260 miles from a full tank. I told her that the gas station was 7 miles away and to figure out if she could make it to the gas station without running out of gas.
Needless to say, she could not figure it out. I was flabbergasted. It was the most basic math in the world. I stopped to think about it for a second and decided to ask the same question but framed differently: If you saw a pair of shoes that normally sold for $300 and instead, they were on sale for only $260, how much money did you save?
No sooner than the last syllable was leaving my mouth, she immediately answered $40. I then asked her if 7 was more than 40 and she replied no... so i asked her again: if she could drive 300 miles on a tank of gas and she had driven 260 miles, would she make it to the gas station that was 7 miles away without running out of gas. She had no idea.
All I could do was sigh. She could obviously do arithmetic but she obviously could not apply it generally.