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Question

Let x1 x2 x3 x4 x5 x6 be a six digit number. The numbers of such numbers if
x1<x2<x3x4<x5<x6 is

A
9C4
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B
9C3
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C
10C4
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D
10C3
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Solution

The correct option is C 10C4
When x1<x2<x3<x4<x5<x6
(Since we have to form 6 digit number, x10)
Numbers can be selected in 9C6 ways and can be arranged in 1 way.

When x1<x2<x3=x4<x5<x6
Numbers can be selected in 9C5 ways and can be arranged in 1 way.

required ways
=9C6+9C5=10C6=10C4
[ nCr1+ nCr= n+1Cr]

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