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# Arnold and Danny are two twin brothers that are celebrating their birt

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Math Expert
Joined: 02 Sep 2009
Posts: 58312
Arnold and Danny are two twin brothers that are celebrating their birt  [#permalink]

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13 Jul 2016, 01:52
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Difficulty:

45% (medium)

Question Stats:

72% (01:25) correct 28% (01:43) wrong based on 48 sessions

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Arnold and Danny are two twin brothers that are celebrating their birthday. The product of their ages today is smaller by 9 from the product of their ages a year from today. What is their age today?

A. 2.
B. 4.
C. 5.
D. 7.
E. 9.

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Intern
Joined: 03 Aug 2015
Posts: 33
Re: Arnold and Danny are two twin brothers that are celebrating their birt  [#permalink]

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13 Jul 2016, 02:24
Let the age be x and after one year the age be x+1.. now as per the given statement :

(X+1)^2 -x^2 = 9

solving we get x=4 hence B
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Joined: 26 Nov 2012
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Arnold and Danny are two twin brothers that are celebrating their birt  [#permalink]

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13 Jul 2016, 02:46
1
Bunuel wrote:
Arnold and Danny are two twin brothers that are celebrating their birthday. The product of their ages today is smaller by 9 from the product of their ages a year from today. What is their age today?

A. 2.
B. 4.
C. 5.
D. 7.
E. 9.

Given Arnold and Danny age be X ( as they are twin brothers will have same age ).

Given the product of their ages is smaller by 9 from the product of their ages a year from today.

The product of their ages as of today be $$X^2$$.

Since we are dealing with past year, then their age is also increased by 1 year.

$$(X + 1)^2$$.

Now difference $$(X + 1)^2$$ - $$X^2$$ = 9.

=> 2X + 1 = 9.

=> 2X = 8. => X = 4.

IMO B is correct option.

OA please...will correct if I missed anything.
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Re: Arnold and Danny are two twin brothers that are celebrating their birt  [#permalink]

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13 Jul 2016, 05:03
Bunuel wrote:
Arnold and Danny are two twin brothers that are celebrating their birthday. The product of their ages today is smaller by 9 from the product of their ages a year from today. What is their age today?

A. 2.
B. 4.
C. 5.
D. 7.
E. 9.

0= a+d-8

a+d = 8

a=d (as they are twin brothers)

a=d=4

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Joined: 04 Mar 2011
Posts: 2817
Re: Arnold and Danny are two twin brothers that are celebrating their birt  [#permalink]

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29 Jan 2018, 10:42
Bunuel wrote:
Arnold and Danny are two twin brothers that are celebrating their birthday. The product of their ages today is smaller by 9 from the product of their ages a year from today. What is their age today?

A. 2.
B. 4.
C. 5.
D. 7.
E. 9.

If we let Arnold's and Danny’s age today = n, then their ages one year from today will be (n + 1). Thus, we have:

n^2 + 9 = (n + 1)(n + 1)

n^2 + 9 = n^2 + 2n + 1

8 = 2n

4 = n

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Re: Arnold and Danny are two twin brothers that are celebrating their birt   [#permalink] 29 Jan 2018, 10:42
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