i really need help with this

Question

Calculate each number below. Which permutation or combination formula can each expression represent?
 


 
a. 7!×12c7=

Answer 1

12! x 12C7

= 12C12 x 12C7

or

= 12C0 x 12C7

= 12! x 12!/7!(12-7)! = 12! x 12!/7!5!

= 12!(12x11x10x9x8)/5x4x3x2x1

= 12!(12x11x3x2)

= 12!(24x33) =12! x 792

= 792(12!)

=792x12x11x10x9x8x7x6x5x4x3x2x1

=792x11880x40320

=9408960x40320

=379,369,267,200

=3.793692672 x 10^11

=about 3.97 x 10^11

= about 4 hundred billion