[cynicalkane]

It's Singapore English. Instead of using tenses, you put a phrase expressing time at the beginning of a clause, a feature borrowed from Chinese. "At first" sets the time and topic of the following clause. Having spent some time in Singapore and HK, I found the Chinese-flavored English to be immediately clear. Actually, if you just guess to substitute the correct verb tense (don't -> didn't), it seems clear to me in ordinary English as well, and I'm not sure where the confusion lies.

The Singaporean government doesn't think Singapore English is a valid thing and wants everyone to learn "good" English. The Singaporean upper class is, as usual, on the government's side, and will complain about the poor English education in their country. That's fine for them, but please be aware that when you say "this is bad English" you are making a cultural and class-based judgment. What you really mean is the math question uses a way of expressing time that is familiar to them but not familiar to you.