# Weird but easy question.

Discussion in 'DAT Discussions' started by gochi, Apr 22, 2007.

1. ### gochi 10+ Year Member

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This is a question from the OAT, but I heard the OAT/DAT are similar, since the sample exams have the exact same reading questions and some mc questions aswell.

If an electron has a mass of 9.709 x 10-31 kg,
and a proton has a mass of 1.672 x 10-27 kg,
approximately how many electrons are
required to have the same mass as one
proton?

A. 150,000
B. 1,800
C. 5.4 x 104
D. 5.4 x 10-4
E. 15 x 10-58

This is what I did...

9.709 x 10-31 : 1.672 x 10-27/1.672 x 10-27 = 9.709 x 10-31/1.672 x 10-27 =1

9.709 x 10-31 - 1.672 x 10-27 = 8.037 x 10-4 ... what am I doing wrong ?

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3. ### Doogie Howser practicing since age 12 5+ Year Member

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mass proton/mass electron. all you need to do is subtract exponents on the 10^x's and divide 9.7/1.67...

but realistically, you should immediately see that it is going to be some "number x 10^4" and since there is only one answer choice with that, move on

4. ### gochi 10+ Year Member

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i did, a (10 x 10-31 / 20 x 10-27)= (10/20) x (-31-(-27)= 1/2 x -4...

5. ### dentstd Fena Gonzales 2+ Year Member

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[nm. erased]

6. ### dentstd Fena Gonzales 2+ Year Member

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But do 1.6E-27 / 9.7 E-31 and you get 1722. Not too too far from 2000.

Jumping the gun to an answer with 10E4 gives you the wrong answer here.

But remember which exponent is bigger, 10^-31 or 10^-27. Doogie made that mistake.

7. ### gochi 10+ Year Member

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If an electron has a mass of 9.709 x 10-31 kg,
and a proton has a mass of 1.672 x 10-27 kg,
approximately how many electrons are
required to have the same mass as one
proton?

but we go (mass of electron/mass of proton)... with reference to the exponents -31-(-27)= -4...what the heck ? whats up with this ?

8. ### dentstd Fena Gonzales 2+ Year Member

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no, you missed what I said. look at the numbers I used, and the order I used them. which one's on top?

an electron's smaller. if you divide Me/Mp, then you get a fraction. 1/1722.

if you divide Mp/Me, you get 1722. (The accepted true number is 1836)

9. ### Doogie Howser practicing since age 12 5+ Year Member

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oh haha whoops....i divided (subtracted) the exponents correctly but not the numbers themselves... silly me, its been a long day.

i hope i don't make that mistake on thursday

10. ### gochi 10+ Year Member

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Yea, but it does not make sense that way.

If an electron has a mass of 9.709 x 10-31 kg,
and a proton has a mass of 1.672 x 10-27 kg,
approximately how many electrons are
required to have the same mass as one
proton?

"ONE PROTON" means --> (Mp/Mp) : (Me/Mp) --? 1 proton : (Me/Mp)

(Me/Me) : (Mp/Me) --> 1 electron : (Mp/Me)

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