Zuo Ge: 70*3=2 10 (yuan)

They originally brought 210+100 = 310 (yuan).

The key is to understand this sentence, which means that the difference of 240- 100 is two of them, so you have to divide by 2. You can draw a picture to understand it. (Draw two lines with two lengths, one is 240, the other is 100, the first one has one left, and the second one has three left. )