Can someone explain probability with permutations and combinations and explain where they are applied?

combination : If the order of numbers  or  operations does not matter

Permutation : when the order of numbers matter ( common example most teachers use : a code of 4 numbers has to be in a certain order and the numbers are from 0 to 9 , how many permutation can you make if you use the number one time)

P=n!/(n-r)!

n! ( are number from 0-9 we have 10 numbers)

r is the number of digits in the code = 4

n!=10*9*8*7*6*5*4*2*1

(n-r)!=(10-4)!=6!=6*5*4*3*2*1

P=5040 ways ( if the order matter)

If the order does not matter

Combination C(n,r)=n!/(n-r)!r!

C(10,4)=(10*9*8*7*6*5*4*2*1)/[(6*5*4*3*2*1)(4*3*2*1)]

answer:

a=9

step-by-step explanation: lmk if you need a explanation

the answer is:

the correct option:

b.

to solve the problem, we need to remember how to operate to simplify exponential expressions using the logarithms.

we are given the equation:

then, using placing logarith with base 7 on both sides of the equation, we have:

so, rounding the obtained result to two decimal places (nearest hundreth), we have:

hence, we have that the correct option:

b.

have a nice day!