Erenmaster
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#1
Report Thread starter 3 months ago
#1
A car driver travels between two cities such that half the distance the speed is 60 km/h. For the remaining distance, half the time the speed is 50 km/h and the other half the time the speed is 80 km/h. If the total distance between the two cities is 450 km, how long took the entire journey?
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Spelunker
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#2
Report 3 months ago
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450/2 = 225
225/60 = 3.75

225/2 = 112.5
112.5/50 = 2.25
112.5/80 = 1.406

3.75 + 2.25 + 1.404 = 7.41 hours

i think this may be the answer but your wording was a bit difficult to understand.
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Erenmaster
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#3
Report Thread starter 3 months ago
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(Original post by Spelunker)
450/2 = 225
225/60 = 3.75

225/2 = 112.5
112.5/50 = 2.25
112.5/80 = 1.406

3.75 + 2.25 + 1.404 = 7.41 hours

i think this may be the answer but your wording was a bit difficult to understand.
I got 7.21 and thx
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DataVenia
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#4
Report 3 months ago
#4
(Original post by Spelunker)
225/2 = 112.5
112.5/50 = 2.25
112.5/80 = 1.406
In this working you've halved the remaining distance (i.e. half of 225 to get 112.5 for each of the last two sections of the journey), but the question says "For the remaining distance, half the time the speed is 50 km/h and the other half the time the speed is 80 km/h."

So, for the second and third sections, if we assume each takes H hours, then we have:
H x 50 km/h + H x 80 km/h = 225 (the second half of the distance).

Solving for H we get:
50H + 80H = 225
130H = 225
H = 225 / 130 = 1.7308 hours (approx)

So, the whole journey is:
3.75 hours at 60 km/h (225 km) +
1.7308 hours at 50 km/h (86.54 km) +
1.7308 hours at 80 km/h (138.46 km)

Those distances total to 450 km. So that's confirms that it works. The times total to 7.21 hours (approx).
Last edited by DataVenia; 3 months ago
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