# math prob

Discussion in 'DAT Discussions' started by tRNA, May 12, 2007.

1. ### tRNA Member

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easy problem but how can u do it in 1min ???

the front tires on a car have circumferences of 3.52ft and the rear tires have circumferences of 5.28ft. On a 4200mile race, how many more revolutions does a front tire make than a rear tire (1mile=5280ft)

a) 2100
b) 8400
c) 2100,000
d) 2800,000
e) 4200,000

3. ### Mia305

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Notice that 5280 and 5.28 are easily divisible...1000 revs/mile

4. ### laundry

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Sure... take a close look at the numbers... c1=3.52 c2=5.28 1ft=5280

1. 5280/5.28 = 1000
2. 5280/3.52 = 1500
3. 1500-1000 = 500
4. 500*4200 = 2,100,000 ...C

iii think...lol

5. ### tRNA Member

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answer is c, but i don't understand, why are you dividing the 5280ft by the 5.28ft? if you are trying to convert the 5.28ft to miles then it should be
5.28ft/5280ft because 1mile=5280ft
and you wrote 1ft=5280(?)....5280what? ft, mile?

6. ### laundry

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oh i meant 1mi=5280 ft

ok, so you need to get the difference between the two.
What i did was a bit faster because essentially you do this:

1rev=3.52 ft for wheel 1.
1rev=5.28 ft for wheel 2.

so, (5280ft/1mi)*(4200mi)*(1rev/3.52ft) - (5280ft/1mi)*(4200mi)*(1rev/5.28ft) = 4200(5280/3.52 - 5280/5.28) = 4200*500 = 2,100,000

Hope this clears it for ya.

cheers

7. ### Dion Junior Member

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This is what I did.
1. First I converted the feet of each of the tires to miles:
- 3.52 ft/5280 ft = 0.0006 miles
- 5.28 ft/5280 ft = 0.001 miles

2. So now we have miles. and miles for a race 4200 miles. Now to find the revs, you divide 4200 miles by each of the above values.
- 4200/0.0006 = 6300000 revs for 3.52 feet
- 4200/0.001 = 4200000 revs for 5.28 feet
3. Then you find the difference in the revolution using the 63000000 and 4200000 values
6300000-4200000 = 2100,000

8. ### laundry

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Dion...why would you ever want to divide that way...that takes an insane amount of time...the problems in math section (for the most part) are geared to finding patterns and playing with numbers. The point of that one was to recognize that 5280/5.28 = 1000 and 5280/3.52=1500. those numbers are a million times easier to work with than your 7th power decimals...IMHO

9. ### Dion Junior Member

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Without a calculator, you already know that 5.28/5280 gives you a 1:1000 ratio 3.52/5280 gives you around a 2:3000's ratio.The 4200 miles given would be on the numerator of each of the ratio values. 4200 divided by (1/1000miles) is the same as 42000 multiplied by 1000 so you just add three zeros to the 4200 and get 420000. 4200 divided by 2/3000s is the same as saying 3,000 times 4200 divided by 2. Then you subtract the difference. Before the last step, you will already be able to automatically eliminate three options.

10. ### tRNA Member

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thank you both that makes alot of sense

11. ### lor

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I had the same problem, time...we all know basic math however we strugggggggle with time...
what did work for me?
I practiced a lot, do the problems again and again
know the following type of problems for your test:
-work problems, they are very easy...you can do them in 15 sec and less
-know the percentage, increase and decrease, income and interest, annual interest problems and etc
-know probability, you'll get the easy ones on the test, toss and fair coin etc
-know that CiVi=CfVf for dilution problems, yes it's chemistry however you could get them in your math section as well exp, 10 OZ of 16% rum....etc
-know your circle, sounded funny, area, volume,...and how you can find r from one and plug in into other one...
-know PEMDAS in Kaplan
just to mention some
Kaplan math section problems are hard so don't time yourself on those BUT DO THEM!!!!
good luck to you!

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