Question 1208621
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Here is a different way to get to the average speed.<br>
The upstream speed is 30-12 = 18 km/h; the downstream speed is 30+12 = 42 km/h.<br>
The ratio of the two speeds is 18:42 = 3:7.  Since the distances are the same, the ratio of the times at the two speeds is 7:3.  So the average speed is<br>
{{{(7/10)(18)+(3/10)(42)=126/10+126/10=252/10=25.2}}}<br>
ANSWER: 25.2<br>