Question 181936
When you want the probability of a OR b OR c ...etc, you musrt
add the probabilities of each event occurring separately
The 1st digit can be 1-9  (0 is not allowed)
The probability of it being a {{{7}}} is {{{1/9}}}
The rest of the digits can be 0-9, so their probability is {{{1/10}}}
The proibability of 1 number being a {{{7}}} is then:
{{{(1/9) + 6*(1/10)}}}
{{{(1/9) + 6*(1/10) = 10/90 + 54/90}}}
{{{10/90 + 54/90 = 64/90}}}
{{{64/90 = 32/45}}} answer