4x+3 because you divide the number of each
Average speed = (total distance traveled)/(total travel time)
= (total distance)/(time of 1st journey<span> + </span>time of 2nd journey<span> + </span>time of 3rd journey)
Let d = the distance between Town A and Town B
<span>So, total distance traveled = </span>3d
Time = distance/speed
time of 1st journey = d/x
time of 2nd journey = d/y
time of 3rd journey = d/z
<span>Total time = </span>d/x<span> + </span>d/y<span> + </span>dz
<span>To simplify, rewrite with common denominator: </span>dyz/xyz<span> + </span>dxz/xyz<span> + </span>dxy/xyz
So, total time = (dyz + dxz + dxy)/xyz
Average speed = (total distance)/(total time)
<span>= </span>3d/[(dyz + dxz + dxy)/xyz]
= (3dxyz)/(dyz + dxz + dxy)
<span>Divide top and bottom by d to get: (3xyz)/(yz + xz + xy)</span>
