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A and B start from a and B at the same time and travel in opposite directions. The two vehicles meet at a distance of 30 km from the midpoint. It is known that it takes 10 hours for a to complete the whole journey and 15 hours for B to complete the whole journey. How many kilometers is the distance between a and B?
A: the distance between a and B is 300 km
A and B run from ab at the same time and meet B at 3 / 7 of the whole journey. A runs 30 kilometers per hour and B takes 7 hours to finish the whole journey
From 3 / 7 of the whole journey from a to B, we can see that B has walked 4 / 7 of the whole journey (1-3 / 7 = 4 / 7). Because the walking time is the same, we can know that B's speed is 4 / 3 of a's, that is 30 * 4 / 3 = 40 km / h. distance = speed x time = 40 X7 km = 280 km
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