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A good thing about this question is that even if you miss the 3 minutes late/early part i.e. if by mistake solve for 3 hours late/early, you will get the same Answer, I suppose.
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Home...........................................Workplace
40 m/h t+3
60 m/h t-3
x m/h t

We know that distance is constant hence

40(t+3) = 60 (t-3) = Distance

t=15
Distance =720

X = Distance/t

hence x=48
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fozzzy
Mr Ben leaves his house for work at exactly 8:00 AM every morning. When he averages 40 miles per hour, he arrives at his workplace three minutes late. When he averages 60 miles per hour, he arrives three minutes early. At what average speed, in miles per hour, should Mr. Ben drive to arrive at his workplace precisely on time?

A) 45
B) 48
C) 50
D) 55
E) 58

Here is what I did

\(\frac{D}{40} - \frac{3}{60} = \frac{D}{60} + \frac{3}{60}\)

Solve this equation to get

\(D = 12\)

\(\frac{D}{40} - \frac{3}{60}\) ( will this equation give me the time?)

we get \(\frac{1}{4}\)

R * T = D

\(\frac{1}{4} * X = 12\)

X = 48

Is this correct?

Can someone tell me is there is any problem if I try and solve it like this:

Let usual time taken = t
Distance = d

Time taken if he's 3 minutes late = t + 3
Time taken if he's 3 minutes early = t - 3

Distance, d = 40 x (t + 3) [when he's late]
Distance, d = 60 x (t - 3) [when he's early]

Hence, 40 x (t + 3) = 60 x (t - 3)
t = 15

if we plug the value of t in any of the equations:
d = 40 x (15 + 3) = 40 x 18 = 720

Average speed = Distance / Time = 720 / 15 = 48
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iaratul
fozzzy
Mr Ben leaves his house for work at exactly 8:00 AM every morning. When he averages 40 miles per hour, he arrives at his workplace three minutes late. When he averages 60 miles per hour, he arrives three minutes early. At what average speed, in miles per hour, should Mr. Ben drive to arrive at his workplace precisely on time?

A) 45
B) 48
C) 50
D) 55
E) 58

Here is what I did

\(\frac{D}{40} - \frac{3}{60} = \frac{D}{60} + \frac{3}{60}\)

Solve this equation to get

\(D = 12\)

\(\frac{D}{40} - \frac{3}{60}\) ( will this equation give me the time?)

we get \(\frac{1}{4}\)

R * T = D

\(\frac{1}{4} * X = 12\)

X = 48

Is this correct?

Can someone tell me is there is any problem if I try and solve it like this:

Let usual time taken = t
Distance = d

Time taken if he's 3 minutes late = t + 3
Time taken if he's 3 minutes early = t - 3

Distance, d = 40 x (t + 3) [when he's late]
Distance, d = 60 x (t - 3) [when he's early]

Hence, 40 x (t + 3) = 60 x (t - 3)
t = 15

if we plug the value of t in any of the equations:
d = 40 x (15 + 3) = 40 x 18 = 720

Average speed = Distance / Time = 720 / 15 = 48

Yes, your approach is correct.
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Bunuel
iaratul

Time taken if he's 3 minutes late = t + 3
Time taken if he's 3 minutes early = t - 3
Yes, your approach is correct.
Wouldn't t+3 be t+3/60?
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