1. Solution: Suppose the distance between the two places is xkm, and the time specified by him is ymin.
From the question, we get the system of equations x/50=y+24;x/75=y-24.
The solution is y=72;x=4800. So the distance between the two places is 4800km.
2. Solution: A originally planned to build xkm every day, and B built ykm every day.
From the meaning of the question, we get the equation system 30(x+y)+10(x+ 0.6)+(50-30-10)×(x+0.6+y+0.4)=200;50(x+y)=200. The solution is x=2.4, y=1.6.
So A originally planned to build 2.4km every day, and B originally planned to build 1.6km every day.
3. According to the meaning of the question, we can get the equation group 5b-5a=2;4a+4b=8, and the solution is a=0.8,b =1.2. So 4a+b=4.4.
4. Dude, what is the second equation equal to. Let me add it.