Thread: linear equations with two unknown

Today I encounter a mathematics problem that is designed for junior students, they are in the topic which teaches the way to set up two linear equations with two unknowns and solve them.

The question is something like:

there are two men, say A and B, they are standing away from each other by 20km, now they walk towards each other (i.e. the "west" one walk toward East, the "east" one walk towards West), 2 hours later they meet each other.

The book didn't state clearly what happens next to the moment they meet. I just understand that it then said the two man separate by some distance now and then they walk towards the SAME direction, (i.e. B is in front of A by some unspecified distance, A and B walks towards the same direction), A then chased up B after 5 hours.

The question is what is their respective speeds?
the book gave a hint that let A walk x km/h and B walk y km/h

if they departed at the same hour and at the same speed the answer is 5km/h.

each hour they approach by xkm + ykm
they will meet aftr 2 hours. therefore, 20km/(xkm/h + ykm/h)=2

hi

if two people walk as a same direction their speed is |X-Y| ..
and if they walk towards each other their speed is x+y ...
so the answer :

x+y = 10 ( Km/h)
x-y = 4 (Km/h)
____________________________
2x=14 -> x=7 (Km/h) -> y=3

hello all

I know the first equation, x+y=10

but this is a topic of linear equation with two unknowns, I don't know the second equation