一道排列组合题--GWD1-7

thumbwings

A certain university will select 1 of 7 candidates eligible to fill a position in the mathematics department and 2 of 10 candidates eligible to fill 2 identical positions in the computer science department.  If none of the candidates is eligible for a position in both departments, how many different sets of 3 candidates are there to fill the 3 positions?

 

A.     42

B.      70

C.     140

D.     165

                                     E.315

sweatfly

 E.

7*[(10*9)/2]=315

lxj19820127

 c(1,7)*c(2,10)=315

thumbwings

thank you !