city a is 100km to the west of city b.david rides a bicycle 15km/h from city a to the west .at the same time,alice drives a car ykm/h from city b to the west.
between david and alice 2 hours (130-2y)
alice catch up with david after 2.5 hours ,find the value .
math fast (100)
2011-12-30 6:22 pm
回答 (2)
2011-12-30 8:11 pm
✔ 最佳答案
A is due west of B 100 kmDavid starts at A to west (away from B) at 15 km/h
David away from B at t hours later: 100 + 15t
Alice starts at B to west (towards A) at y km/h
Alice away from B at t hours later: yt
Alice catches up with David at 2.5 h
Alice away from B at 2.5 hours later: 2.5y
David away from B at 2.5 hours later: 100+15(2.5)
thus,
2.5y = 100 + 15(2.5)
y = 55 km/h
2011-12-30 8:57 pm
A is due west of B 100 km
David starts at A to west (away from B) at 15 km/h
David away from B at t hours later: 100 + 15t
Alice starts at B to west (towards A) at y km/h
Alice away from B at t hours later: yt
Alice catches up with David at 2.5 h
Alice away from B at 2.5 hours later: 2.5y
David away from B at 2.5 hours later: 100+15(2.5)
so,
2.5y = 100 + 15(2.5)
y = 55 km/h
David starts at A to west (away from B) at 15 km/h
David away from B at t hours later: 100 + 15t
Alice starts at B to west (towards A) at y km/h
Alice away from B at t hours later: yt
Alice catches up with David at 2.5 h
Alice away from B at 2.5 hours later: 2.5y
David away from B at 2.5 hours later: 100+15(2.5)
so,
2.5y = 100 + 15(2.5)
y = 55 km/h
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