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Permutations with numbers

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Permutations with numbers

by zaarathelab » Wed Dec 28, 2011 9:15 am
How many numbers greater than 1000000 can be formed by using the digits 1, 2, 0, 2, 4, 2, 4?

a) 420
b) 360
c) 120
d) 600
e) 900
Last edited by zaarathelab on Wed Dec 28, 2011 9:38 am, edited 1 time in total.
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by kanwar86 » Wed Dec 28, 2011 9:34 am
zaarathelab wrote:How many numbers greater than 1000000 can be formed by using the digits 1, 2, 0, 2, 4, 2, 4?

a) 420
b) 360
c) 120
d) 600
e) 900

My way

[spoiler]Let's say the 7 digits represent 7 boxes. The first box can be filled in 6 ways (0 can't be there)
The second box in 6 ways
The third in 5 ways......so on. therefore - 6*6*5*4*3*2*1

But there are two 4s and three 2s

Therefore,

6*6*5*4*3*2*1/ (3! * 2!)

= 900

But the answer is B (360). In the above method, where am i going wrong?[/spoiler]
6*6*5*4*3*2*1/ (3! * 2!)
=12*3*5!/12
=3.5!
=3.120
=360= Your answer
Regards

Kanwar

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by zaarathelab » Wed Dec 28, 2011 9:40 am
Thanks Kanwar! I think i should get some sleep :roll:
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