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# The average speed of a car decreased by 3 miles per hour

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Manager
Joined: 09 Jan 2007
Posts: 240
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The average speed of a car decreased by 3 miles per hour [#permalink]  05 Mar 2007, 06:59
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The average speed of a car decreased by 3 miles per hour every successive 8-minute interval. If the car traveled 4.8 miles in the fourteenth 8-minute interval, what was the average speed of the car, in miles per hour, in the first 8-minute interval?
a) 66
b) 69
c) 72
d) 75
e) 78

Last edited by rdg on 05 Mar 2007, 08:30, edited 1 time in total.
Senior Manager
Joined: 18 Feb 2007
Posts: 253
Followers: 1

Kudos [?]: 1 [0], given: 0

Re: PS - Average Speed [#permalink]  05 Mar 2007, 07:53
rdg wrote:
The average speed of a car decreased by 3 miles per hour every successive 8-minute interval. If the car traveled 4.8 miles in the fourteen 8-minute interval, what was the average speed of the car, in miles per hour, in the first 8-minute interval?
a) 66
b) 69
c) 72
d) 75
e) 78

i cant see how the rates can be so high if the avg rate is 2.57 mph..
Senior Manager
Joined: 18 Feb 2007
Posts: 253
Followers: 1

Kudos [?]: 1 [0], given: 0

you have written:
"fourteen 8-minute interval,"

i interpreted this as "in the fourteen 8-minute interval(s)"

did you actually mean to type "fourteenth?"

if so, please make the neccessary correction

i assume that is what you meant
(r-3*13)(8/60) = 4.8
r = 72
Manager
Joined: 09 Jan 2007
Posts: 240
Followers: 1

Kudos [?]: 7 [0], given: 0

you have written:
"fourteen 8-minute interval,"

i interpreted this as "in the fourteen 8-minute interval(s)"

did you actually mean to type "fourteenth?"

if so, please make the neccessary correction

i assume that is what you meant
(r-3*13)(8/60) = 4.8
r = 72

You are right, it is fourteenth. It's typo mistake. Corrected.
Manager
Joined: 09 Jan 2007
Posts: 240
Followers: 1

Kudos [?]: 7 [0], given: 0

you have written:
"fourteen 8-minute interval,"

i interpreted this as "in the fourteen 8-minute interval(s)"

did you actually mean to type "fourteenth?"

if so, please make the neccessary correction

i assume that is what you meant
(r-3*13)(8/60) = 4.8
r = 72

Your approch is right but the calculation is wrong. It should be r = 75
Senior Manager
Joined: 18 Feb 2007
Posts: 253
Followers: 1

Kudos [?]: 1 [0], given: 0

rdg wrote:
you have written:
"fourteen 8-minute interval,"

i interpreted this as "in the fourteen 8-minute interval(s)"

did you actually mean to type "fourteenth?"

if so, please make the neccessary correction

i assume that is what you meant
(r-3*13)(8/60) = 4.8
r = 72

Your approch is right but the calculation is wrong. It should be r = 75

oh yeah..oops.
13*3 is 39 not 36..duhhhh!!!
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