No of people not from their neighborhood=25-20=5
total contact s=25
therefore probability to call a person not from his neighborhood=5/25=1/5
therefore P=1/5
GP = 1/2 , 1/4 , 1/8 , 1/16
1st) the common ratio is (1/4 : 1/2 ) = 1/2, so r =1/2
2nd) the sum of a GP is:
S= a(1-rⁿ)/(1-r)
S=(1/2).[1-(1/2)⁴]/(1-1/2) = 15/16
Answer: a $0.23
explanation: 2.76 divided by 12 is 0.23
to check: 0.23 X 12 = 2.76
