Question

the figures 4,5,6,7,8 are written in every possible order.the number of numbers greater than 56000 is

Answer 1

First, let's find all the combinations:

5! = 120.

Since the formula is

n(n-1)(n-2)(n-3)...(n-r),

where r is

(the number of positions)-1,

so now we see: combinations which don't accept 4's at the start and 54's

4! = 24
3! = 6
24+6 = 30

and we have:

120-30 = 90.