Thread: 1-1

Determine the # of 1-1 correspondences in 2 sets each containing 5 elements, 6 elements, n elements.

Hello fifthrapiers!
If
A={x1,x2,x3.....xM}
B={y1,y2,y3.....yN}
For 1-1 functions from A to B
Here
x1 can take N images
x2 can take N-1 images
x3 can take N-2 images
.............
...........
xM can take N-M+1 images
Thus no. of mappings =N(N-1)(N-2).... (N-M+1)

= (N)!/(N-M)! , if N>=M
else= 0 , if N<M
Your Question Has N=M.