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Mike drove 30

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Mike drove 30

by sanju09 » Sat Jun 19, 2010 2:48 am
Mike drove 30 miles, at a constant speed, for t hours and then drove y miles, at another constant speed, for 1 hour and 15 minutes. What was his average speed, in miles per hour, for the whole journey?
(A) (30/t + y/1.25) / 2
(B) (30 + y) / (t + 1.25)
(C) (30 + y) / t
(D) (30 + y) / 1.25
(E) (30 + y) / 2(t + 1.25)
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by amising6 » Sat Jun 19, 2010 2:53 am
sanju09 wrote:Mike drove 30 miles, at a constant speed, for t hours and then drove y miles, at another constant speed, for 1 hour and 15 minutes. What was his average speed, in miles per hour, for the whole journey?
(A) (30/t + y/1.25) / 2
(B) (30 + y) / (t + 1.25)
(C) (30 + y) / t
(D) (30 + y) / 1.25
(E) (30 + y) / 2(t + 1.25)
let constant speed for forst part of journey=s1=30/t
constant speeed for second part of journey s2=y/(5/4) s2=4y/5
so average speed =s1+s2/2
so (30/t+y/1.25)/2
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by kvcpk » Sat Jun 19, 2010 2:54 am
sanju09 wrote:Mike drove 30 miles, at a constant speed, for t hours and then drove y miles, at another constant speed, for 1 hour and 15 minutes. What was his average speed, in miles per hour, for the whole journey?
(A) (30/t + y/1.25) / 2
(B) (30 + y) / (t + 1.25)
(C) (30 + y) / t
(D) (30 + y) / 1.25
(E) (30 + y) / 2(t + 1.25)
avg speed = total dist /total time

total dist = 30 + y
total time = t + 1.25

so avg speed = 30 +y /t + 1.25

B
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by sanju09 » Sat Jun 19, 2010 2:57 am
amising6 wrote:
sanju09 wrote:Mike drove 30 miles, at a constant speed, for t hours and then drove y miles, at another constant speed, for 1 hour and 15 minutes. What was his average speed, in miles per hour, for the whole journey?
(A) (30/t + y/1.25) / 2
(B) (30 + y) / (t + 1.25)
(C) (30 + y) / t
(D) (30 + y) / 1.25
(E) (30 + y) / 2(t + 1.25)
let constant speed for forst part of journey=s1=30/t
constant speeed for second part of journey s2=y/(5/4) s2=4y/5
so average speed =s1+s2/2
so (30/t+y/1.25)/2
Do never confuse between arithmetic mean of speeds and the average speed.
The mind is everything. What you think you become. -Lord Buddha



Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com
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by amising6 » Sat Jun 19, 2010 2:59 am
sanju09 wrote:
amising6 wrote:
sanju09 wrote:Mike drove 30 miles, at a constant speed, for t hours and then drove y miles, at another constant speed, for 1 hour and 15 minutes. What was his average speed, in miles per hour, for the whole journey?
(A) (30/t + y/1.25) / 2
(B) (30 + y) / (t + 1.25)
(C) (30 + y) / t
(D) (30 + y) / 1.25
(E) (30 + y) / 2(t + 1.25)
let constant speed for forst part of journey=s1=30/t
constant speeed for second part of journey s2=y/(5/4) s2=4y/5
so average speed =s1+s2/2
so (30/t+y/1.25)/2
Do never confuse between arithmetic mean of speeds and the average speed.
meaning average speed is total distance travelled by total time taken

so B
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