Question 550170
the answer is P(5, 2) = 5!/(5-2)! = 5!/3!= (5*4*3*2*1)/(3*2*1)=5*4 = 20

you can also find these two digits  numbers by using a Cartesian Coordinate system if you put all numbers (3,4,5,6 and 7) on x and y axis, than find all pairs

after you find all pairs, you need to EXCLUDE pairs (3,3),(4,4),(5,5), (6,6) and (7,7)