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Some doubts in PS and DS

Problem Solving — algebra and arithmetic (GMAT Focus Edition)
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Some doubts in PS and DS

by Caps » Tue Feb 20, 2007 9:58 am
Can someone help me on this?? need explainations:

PS 1
How many integeres between 324700 and 458600 have a tens digit 1 and a units digit 3?

PS 2
In n is an integer which of the following CANNOT be a factor of 3n+4?
a)4 b)5 c)6 d)7 e)8

DS 1
If a and b are positive integeres what is the value of a+b?
1) a/b = 5/8
2) The greatest common divisor of a and b is 1


tnks for your help guys
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by ktr32 » Tue Feb 20, 2007 10:20 am
I will try to answer the questions 1 & 2, correct me if I am wrong.

Q1.
looking for how many times 13 appears between 324700 and 458600. 13 will only appear once every 100 number so: subtract 324700 from 458600 , then divide by 100, to how many times 13 will appear

458600 - 324700 = 133900 => 133900/100 = 1339, therefore the number 13 would appear 1339 times.


Q2. Best way is to plug in numbers for n, try {1,2,3,4,5} this should good picture.

3(1) + 4 = 7
3(2) + 4 = 10
3(3) + 4 = 13
3(4) + 4 = 16

From this you can eliminate a, b d, e thus only leaving c as your answer.
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by banona » Tue Feb 20, 2007 2:58 pm
here is my thoughts about the third question,
DS 1
If a and b are positive integeres what is the value of a+b?
1) a/b = 5/8
2) The greatest common divisor of a and b is 1

1- first statement ;isnot suffisant at all

2- second statement tells that the GCF of both a and b is 1, it is also insuffisant but we cab conclude that a and b are both products of different prime numbers ( I mean no factor of a is alsoa factor of be neither is it divior of it)

combining 1 and 2, we conclude that 5/8 is not a simplified fraction of a/b, therfore, a is 5 and b must be 8.

So a+b = 13

I hope I am right
I appologize for my Frenchy-English.
I am working on it.
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by Stacey Koprince » Mon Feb 26, 2007 10:57 pm
Nice job guys! Caps, when posting questions, please post the full text of the question (eg, for the first PS question, please post the answers). Choosing the best solving strategy is sometimes only possible when you know what the answers are.
Please note: I do not use the Private Messaging system! I will not see any PMs that you send to me!!

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