math
posted by anonymous .
there are 7 boys and 6 girls willing to serve on a committee. how many 7member committees are possible if a committee is to contain:
a) 3 boys and 4 girls
b) at least one member of each sex?
thank in advance!!

a) What is C(7,3) x C(6,4) ?
b) with no restriction  C(13,7)
all girls = C(6,4)
all boys = C(7,3)
exclude the all boys/girs from the total. 
i did them but i got the wrong answers
for (a), the answer must be 525 and
for (b), the answer must be 1715
i got the rite answer for letter b though, by doing my own method 
oh and thanks :]