Question 764478
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This is the same as asking "In how many ways can you choose 4 books out of a set
of 10 books?" Because once you choose a set of 4, the other set is automatically 
6.

So the number of ways is C(10,4) (which is also equal to C(10,6) since C(N,n) 
is the same as C(N,N-n))

= {{{(10*9*8*7)/(1*2*3*4)}}} = 210 ways.

:)
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