Copilot is bad at math

It all started with a repost of the classic example of a teacher screw-up:

On a test for third grade, one of the questions was “It took Marie 10 minutes to saw a board into 2 pieces. if she works just as fast, how long will it take her to saw another board into 3 pieces?“

The student answered correctly – 20 minutes, and the teacher “corrected” it with the wrong answer – 15.

The I decided to ask the same question to Copilot:

So far, so good. Correct answer and reasoning, although the formula that is displayed is utter nonsense.

Next, I tried to ask the derived question “It took Marie 10 minutes to saw a board into 3 pieces. if she works just as fast, how long will it take her to saw another board into 4 pieces?“. Any person who understood the first question and answered it correctly should have no trouble to apply the same logic to the second one and answer it correctly, right? Not so with Copilot.