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Vectors

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8 Apr 2008 11:27:01 IST

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ashish banga

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8 Apr 2008 11:30:04 IST

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in qs....wen u r given like

find the sum of numbers formed by using n numbers

eg. find the sum of numbers formed by taking all da given digits of 2,3,4,5

its a very simple trick....

the formula is

(sum of all da digits) x (n - 1)! x (1.1.1.1............n times)

where n is no. of digits

like here in dis case , n = 4 (2 , 3 , 4 , 5.......4 no.s)

so its simple

(2 + 3 + 4 + 5) (3)! (1111)...............as n = 4 so 1111

14 x 6 x 1111 = 93324

dese typeof qs can be asked in JEE.....infact dis example is a JEE qs....

cheers!!!!!!!!!!

Rahul Raghavendra

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8 Apr 2008 11:58:48 IST

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is this applicable to every series

SRM

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Joined: 25 Feb 2008

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8 Apr 2008 12:07:53 IST

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Hey @ashish_banga.... have you got any more simple tricks up your sleeve..... if you do ...please share...

ashish banga

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8 Apr 2008 12:11:26 IST

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another one
find the sum of all 5-digit numbers that can be formed using the digits 1,2,3,4,5 if repetition is not allowed."

As choosing a set of 5 out of {1,2,3,4,5} is possible in only one way

12345

So number of all different numbers can be formed by this set is 5! = 120

As the mean digit in each column is 3, each number is 33333, on average. Hence the sum is 120 X 33333= 3,999,960.

this is when repitition is not allowed

ashish banga

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8 Apr 2008 12:12:44 IST

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But if there are 6 digits ( as in 1,2,3,4,5,6) , then what?

For 6 numbers, total possible numbers are 6! = 720

take half of the the average numbers = 333,333 and other half = 444,444

So the sum can be S = 360 x 333,333 + 360 x 444,444

kshitij verma

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8 Apr 2008 12:30:42 IST

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http://www.goiit.com/posts/list/general-tricks-mania-43996.htm

give the source too , dont copy :)

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