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What is the value of (11! - 10!)/9!
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25 Apr 2019, 03:33
25 Apr 2019, 03:33
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Difficulty:
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Question Stats:
91% (00:45) correct
9%
(01:15)
wrong
based on 114
sessions
What is the value of (11! - 10!)/9!
(A) 99
(B) 100
(C) 110
(D) 121
(E) 132
(A) 99
(B) 100
(C) 110
(D) 121
(E) 132
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Joined: 12 Sep 2015
Posts: 6803
Given Kudos: 799
Location: Canada
Re: What is the value of (11! - 10!)/9!
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25 Apr 2019, 08:09
25 Apr 2019, 08:09
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Bunuel wrote:
What is the value of (11! - 10!)/9!
(A) 99
(B) 100
(C) 110
(D) 121
(E) 132
(A) 99
(B) 100
(C) 110
(D) 121
(E) 132
Useful (and often-tested) concept: \(\frac{a - b}{c}=\frac{a}{c}-\frac{b}{c}\)
So, \(\frac{11! - 10!}{9!}=\frac{11!}{9!}-\frac{10!}{9!}\)
\(=\frac{(11)(10)(9)(8)(7)(6)(5)(4)(3)(2)(1)}{(9)(8)(7)(6)(5)(4)(3)(2)(1)}-\frac{(10)(9)(8)(7)(6)(5)(4)(3)(2)(1)}{(9)(8)(7)(6)(5)(4)(3)(2)(1)}\)
\(= (11)(10)-(10)\)
\(= 110-10\)
\(= 100\)
Answer: B
Cheers,
Brent
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What is the value of (11! - 10!)/9!
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25 Apr 2019, 03:47
25 Apr 2019, 03:47
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--> (11!/9!) - (10!/9!)
= (10x11) - (10) [all values from 1 to 9 get cancelled out in Nr. and Dr.]
= 110 - 10
= 100
Hope this is correct
= (10x11) - (10) [all values from 1 to 9 get cancelled out in Nr. and Dr.]
= 110 - 10
= 100
Hope this is correct
