TBR Magnitude Estimation Trick

[elusiveCHILD]

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Does anyone feel very comfortable with this trick and is willing to go over a simple example relating to this? Thanks in advance!

 

[elusiveCHILD]

For example in TBR another example problem ( 1.1.b)

How fast is a car traveling in miles per hour if it has a speed of 0.02906 km/s? 1 mile= 1609.38 m?

a) 0.018miles/ hr
b) 1.1 miles/ hr
c) 65 miles/ hr
d) 780 miles/ hr

1) Crossed out a and d because these values are too large or small.
2) Now I'm left with b or c

So initially I changed both numbers to scientific notation

1) 0.02906 km/s==> 2.906 x 10^-2
2) 1609.38 m==> 1.60938 x 10^3

Then I am just lost after that... am I on the right track? Thanks in advance!

 

[Patassa]

For example in TBR another example problem ( 1.1.b)

How fast is a car traveling in miles per hour if it has a speed of 0.02906 km/s? 1 mile= 1609.38 m?

a) 0.018miles/ hr
b) 1.1 miles/ hr
c) 65 miles/ hr
d) 780 miles/ hr

1) Crossed out a and d because these values are too large or small.
2) Now I'm left with b or c

So initially I changed both numbers to scientific notation

1) 0.02906 km/s==> 2.906 x 10^-2
2) 1609.38 m==> 1.60938 x 10^3

Then I am just lost after that... am I on the right track? Thanks in advance!

I'm sorry I see that I mixed up your question with the thread that was asking about limiting cases technique. Ignore what I said about that.

 

[elusiveCHILD]

Thanks so much. I just need to practice more dimensional analysis problems then.

 

[Patassa]

Thanks so much. I just need to practice more dimensional analysis problems then.

It's just a fancy word for converting units or correctly matching up units, it's just like doing stoichiometry. Pretty straight forward

.03 km/s * 1000m/km * 1mile/1609m * 3600s/ hr = # mile/hr

 

[rguil15]

Wn

 

[drechie]

does anyone have a quicker way to go about the magnitude estimation without doing the dimensional analysis? there seems to be a quicker way to use this technique.

 

[Blueprint MCAT Tutor]

It's just a fancy word for converting units or correctly matching up units, it's just like doing stoichiometry. Pretty straight forward

.03 km/s * 1000m/km * 1mile/1609m * 3600s/ hr = # mile/hr

Yes but I would suggest, given the way the answer choices are spread out that you can afford to estimate MUCH more.

0.03km/s

First if there's 3600s/hr, round that down to 3000. So take the original value, triple it, and move the decimal three places:

90km/hr

Then, you know that a km and a mile are (relatively) close to each other in value (less than 10x apart) and choice (C) is the only one that's got the order of magnitude right.

I'm not familiar with the particular "technique" being asked about in the OP, but I'd suggest that the big general takeaway point is this: before doing any calculations on the MCAT, look at the answer choices to see how far apart they are so you know how merciless you can be with your rounding off.