Please help with this word problem!

[lillybeth]

Hey guys! I'm doing review for a Test, and I would appreciate it if someone could help me with this problem I ran into:

Sharon is taking a bus from Baltimore, Maryland, to Washington D.C. If the distance is 40 miles and the estimated time of travel is 1 hour, what is the average rate at which the bus travels? (Hint: Use the formula d=rt)
The part I don't get is where to plug in the numbers. Please help!

Choices:
a). 60 mph
b). 30 mph
c). 25 mph
d). 40 mph

Thanks for the help!

 

[JeffM]

Hey guys! I'm doing review for a Test, and I would appreciate it if someone could help me with this problem I ran into:

Sharon is taking a bus from Baltimore, Maryland, to Washington D.C. If the distance is 40 miles and the estimated time of travel is 1 hour, what is the average rate at which the bus travels? (Hint: Use the formula d=rt)
The part I don't get is where to plug in the numbers. Please help!

Choices:
a). 60 mph
b). 30 mph
c). 25 mph
d). 40 mph

Thanks for the help!

Lillybeth

In the formula, what does d stand for, what does r stand for, and what does t stand for?

Given all that, do you now know or can you make an eductaed guess as to where the numbers for time and distance are to go?

 

[Deleted member 4993]

Hey guys! I'm doing review for a Test, and I would appreciate it if someone could help me with this problem I ran into:

Sharon is taking a bus from Baltimore, Maryland, to Washington D.C. If the distance is 40 miles and the estimated time of travel is 1 hour, what is the average rate at which the bus travels? (Hint: Use the formula d=rt)
The part I don't get is where to plug in the numbers. Please help!

Choices:
a). 60 mph
b). 30 mph
c). 25 mph
d). 40 mph

Thanks for the help!

You are given a formula. You need to use it (plug-in). You need to know:

What is 'd'? What is the unit (dimension) of 'd'?

What is 'r'? What is the unit (dimension) of 'r'?

What is 't'? What is the unit (dimension) of 't'?

Do you know the answers to the above questions?

 

[lillybeth]

Lillybeth

In the formula, what does d stand for, what does r stand for, and what does t stand for?

Given all that, do you now know or can you make an eductaed guess as to where the numbers for time and distance are to go?

I know that d= distance, r= rate, and t= time, so it would be 40=r1?

do I just divide 40 by one to find out what r is?
p.s. I already found out the answer was 40 mph, but I'm wondering if I did the problem right.

 

[JeffM]

I know that d= distance, r= rate, and t= time, so it would be 40=r1?

do I just divide 40 by one to find out what r is?
p.s. I already found out the answer was 40 mph, but I'm wondering if I did the problem right.

Yes.

\(\displaystyle d = r * t \longleftrightarrow r = \dfrac{d}{t} \longleftrightarrow t = \dfrac{d}{r}.\)

By manipulating this little formula, you can determine any one of three variables from the other two. Very simple.

Subhotosh Khan mentioned dimensions. Dimensional analysis is a technique that you can use to make sure that you apply a formula correctly. It becomes VERY handy in the physical sciences

Rate is frequently measured in units of miles per hour so \(\displaystyle r = \dfrac{40\ miles}{1\ hour} = 40\ miles/hour.\)

You ended up with an answer that had the right units so that is confirmation that you used the formula correctly.

If you had calculated \(\displaystyle r = \dfrac{1\ hour}{40\ miles} = .025\ hours/mile.\)

But we do not measure speeds as hours per mile so you used the formula incorrectly.

All clear now?

 

[lillybeth]

Yes.

\(\displaystyle d = r * t \longleftrightarrow r = \dfrac{d}{t} \longleftrightarrow t = \dfrac{d}{r}.\)

By manipulating this little formula, you can determine any one of three variables from the other two. Very simple.

Subhotosh Khan mentioned dimensions. Dimensional analysis is a technique that you can use to make sure that you apply a formula correctly. It becomes VERY handy in the physical sciences

Rate is frequently measured in units of miles per hour so \(\displaystyle r = \dfrac{40\ miles}{1\ hour} = 40\ miles/hour.\)

You ended up with an answer that had the right units so that is confirmation that you used the formula correctly.

If you had calculated \(\displaystyle r = \dfrac{1\ hour}{40\ miles} = .025\ hours/mile.\)

But we do not measure speeds as hours per mile so you used the formula incorrectly.

All clear now?

Yup! Thanks for the help Jeff! (and anyone else who posted here)