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Re: If r is an integer, and 700 < 10!/(10-r)!<1,000, then r=
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21 Nov 2017, 18:37
MathRevolution wrote:
[GMAT math practice question]
If r is an integer, and \(700 < \frac{10!}{(10-r)!}<1,000\), then r=
A. 1 B. 2 C. 3 D. 4 E. 5
Hi....
\(\frac{10!}{(10-r)!}=10*9*8..*(10-(r-1)\) Now it is given this value is more than 700 and less than 1000 10*9*8=720 So 10-(r-1)=8.....r-1=10-8=2....r=2+1=3 C
_________________
Re: If r is an integer, and 700 < 10!/(10-r)!<1,000, then r=
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22 Nov 2017, 04:27
MathRevolution wrote:
[GMAT math practice question]
If r is an integer, and \(700 < \frac{10!}{(10-r)!}<1,000\), then r=
A. 1 B. 2 C. 3 D. 4 E. 5
An easy way to solve this question is to plug in the answers given, calculate the value of \(\frac{10!}{(10-r)!}\) and see whether it satisfies or violates the inequality in the problem prompt.
A/\(r = 1\) This gives us: \(\frac{10!}{(10-r)!} = \frac{10!}{9!} = 10\). This violates the inequality given in the problem prompt. B/ \(r = 2\) This gives us: \(\frac{10!}{(10-r)!} = \frac{10!}{8!} = 10*9 = 90\). This also violates the inequality given in the problem prompt. C/ \(r = 3\) This gives us: \(\frac{10!}{(10-r)!} = \frac{10!}{7!} = 10*9*8 = 720\). This satisfies the inequality given in the problem prompt, therefore, this is our answer (we can afford to stop here since this is not a DS question nor is the unknown a polynomial/non-integer with multiple potential values).
Re: If r is an integer, and 700 < 10!/(10-r)!<1,000, then r=
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06 Feb 2018, 10:55
chetan2u wrote:
MathRevolution wrote:
[GMAT math practice question]
If r is an integer, and \(700 < \frac{10!}{(10-r)!}<1,000\), then r=
A. 1 B. 2 C. 3 D. 4 E. 5
Hi....
\(\frac{10!}{(10-r)!}=10*9*8..*(10-(r-1))\) Now it is given this value is more than 700 and less than 1000 10*9*8=720 So 10-(r-1)=8.....r-1=10-8=2....r=2+1=3 C
Hi Chetan,
Can you please explain how did you derive \(\frac{10!}{(10-r)!}=10*9*8..*(10-(r-1)\)
gmatclubot
Re: If r is an integer, and 700 < 10!/(10-r)!<1,000, then r= &nbs
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06 Feb 2018, 10:55
close
74% (01:28) correct 
