Earlier quoted context omitted.
Multiplication problems are not language problems. There is no data in the training set where there is a likely probability of the next token in the "86 * 0.0007 =" sentence being correct. People need to stop treating ChatGPT as a computation engine. It is not wolfram alpha. It is not google. It is fancy autocomplete trained on a large subset of the internet.
You can use this for that: https://huggingface.co/spaces/JavaFXpert/Chat-GPT-LangChain (GPT + WolframAlpha + Whisper)
EDIT: turns out, the latest version of chatGPT knows the answer. They also fixed the answer to another famous trick question("The son of my father, but not my brother. Who is that?")