SOLUTION: Two men A and B walk from P to Q a distance of 'D' at S1 and S2 km per hour. B reaches Q,returns immediately and meets A at R,find the distance from P to Q. I need an explanation

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Question 879100: Two men A and B walk from P to Q a distance of 'D' at S1 and S2 km per hour. B reaches Q,returns immediately and meets A at R,find the distance from P to Q. I need an explanation for this rather than mere formula. thank you in advance.
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
Two men A and B walk from P to Q a distance of 'D' at S1 and S2 km per hour. B reaches Q,returns immediately and meets A at R,find the distance from P to Q.
:
When they meet:
A: travels (D-R)
B: travels (D+R)
:
Their travel time is the same; write a time equation: time = dist/speed
%28D-R%29%2F%28S1%29 = %28D%2BR%29%2F%28S2%29
Cross multiply
S2(D-R) = S1(D+R)
S2D - S2R = S1D + S1R
S2D - S1D = S1R + S2R
Factor out D & R
D(S2-S1) = R(S1+S2)
D = %28R%28S1%2BS2%29%29%2F%28%28S2-S1%29%29 is the distance from P to Q