How many arrangements of four 3’s two 1’s and two 2’s are there in which 1 occurs before 2?
A
210
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B
420
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C
105
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D
315
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Solution
The correct option is A 210 Total Number of arrangements =∠8∠4∠2∠2=420
Since there are two 1 ‘s, two 2’s, the number of arrangements say x in which 1 occurs before 2 is same as the 2 occurs before 1.2x=420⇒x=210