Question 877648

a certain journey took 40 min to complete. if half of the distance was travelled at an average speed of 100 km/h and the other half at an average speed of 60 km/h, what was the length of the journey? i tried 180 km/h divided by 2 and then i got lost
<pre>
Let distance of entire journey be D
Then half of journey = {{{(1/2)D}}}, or {{{D/2}}}
Then time taken on 1st half of journey = {{{(D/2)/100}}}, or {{{(D/2) * (1/100)}}}, or {{{D/200}}}
Time taken on second half of journey = {{{(D/2)/60}}}, or {{{(D/2) * (1/60)}}}, or {{{D/120}}}
Since time taken on entire journey = 40 mins, or {{{40/100}}}, or {{{2/5}}} hour, then we get: {{{(D/200) + (D/120) = 2/5}}} 
3D + 5D = 240 ------- Multiplying by LCD, 600
8D = 240 
Distance, or {{{D = 240/8}}}, or {{{highlight_green(highlight_green(D = 30))}}} km
You can do the check!! 

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