The number of ways of choosing 4 digits from 10 digits without replacement ( order is important) is
. This is the number of all possible permutations of choosing 4 from 10. The first 4 numbers of your phone number is a unique 4 digit number(4 different digits). The required probability is

Answer:
can you explain more freely about question I did not understand sorry for comments in answet
Both of the other angles are 40° because a triangle has a total angle of 180° and an isosceles triangle means that at least two of the sides have to be the same length (two angles must be the same)
180 - 100= 80
80 ÷ 2 = 40