For a group photograph, 3 boys & 2 girls stand in a line in all possible ways. How many photos could be taken if each photo corresponds to each such arrangement ?
BG--GB
BBG--BGB--GBB
BBGG--BGBG--BGGB--A--B--C
BBBGG--BBGBG--BBGGB--D--E--F--G...
The number of permutaions of "n" things, taken all at a time,
"p" things are of one kind, "q" of another kind, "r" of a third kind,
and the rest different is nP(pqr) = n!/(p!q!r!).
Therefore, nP = n(pq) = = 5!(3!x2!) = ?
