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# Compared to what other are posting, I would like to start

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Intern
Joined: 26 Jan 2004
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Compared to what other are posting, I would like to start [#permalink]  01 Apr 2004, 09:43
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Compared to what other are posting, I would like to start with simple ones (at least to most of you guys here) but they did pose problem to me. Please bear with me.

If d is a positive integer, is sqrt(d) > 15?

1. d is divisible by 25
2. d is divisible by 40
CEO
Joined: 15 Aug 2003
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Re: DS- Positive Integer [#permalink]  01 Apr 2004, 10:10
asagem99 wrote:
Compared to what other are posting, I would like to start with simple ones (at least to most of you guys here) but they did pose problem to me. Please bear with me.

If d is a positive integer, is sqrt(d) > 15?

1. d is divisible by 25
2. d is divisible by 40

Not a problem , gem. No problem is too simple or too hard here

Intern
Joined: 31 Mar 2004
Posts: 28
Location: texas
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i think it is both i.e c...for the following reasons

1. if d is divisible by 25

try 100 and sqrt of 100 is 10.. < 15

try 600 and sqrt of 600 is > 15 therefore insufficient

2. if d is divisible by 40

try 80 and sqrt of 80 ....<15

try 40000 and sqrt of 40000 is >15...therefore insufficient

however if you use both, the L.C.M of 40 and 25 is 2^3 * 5^2 = 200

so for any number that divides 200 without any renainders, the sqrt will be greater than 15.

try 400 and sqrt of 400 is 20...etc all >15
Director
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Hallo Kunbol, i can not get what is your answer. is it C) or E)?Thanks
Director
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If your answer is C) then , as you have pointed out D=200 and sqrt200<15 but on the other hand 400 is also divisible by 25 and 40 and sqrt400>15. I would go with E)
Intern
Joined: 31 Mar 2004
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i guess you are right then..i was thinking of that..but i assumed.....i agree with you..seems to be E
thanks
Intern
Joined: 26 Jan 2004
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Thanks Praetorian for your encouraging words. My math skills are very rusty due to long break and I have short time to prepare. I see very smart people posting here with good questions, most of which I cannot answer but I am trying hard to pick lot of stuff in short time.

Official answer is E but in a hurry I picked C after just finding one integer which satisfied the stem(400) but could not figure out there could be more than one satisfying stem. After review of above I would have approached the problem in the following manner.

1. Least integer that can satisfy sqrt(d) > 15 is 16. Thus least d can be 256. Closest integer greater than 256 that is divisible by 25 is 400. Also 10000 satifies and thus insufficient.

2. d is divisible by 40 which again is satisfied by 400 or 10000. Thus insufficient.
Combining still d can be 400 or 10000.
Is there more structured approach to these kind of problems. How much time I need to spend to plug numbers approach vs. more formalized approach which obviously needs better command of numbers theory I guess.
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