The series of differences between consecutive prime numbers is represented as Cp1, Cp2, Cp3, .... Cpn , Whare Cp1 is the difference between the second and the first prime number. Find the sum of series when n = 23, given that the 23rd prime number is 83 ?

A 87

B 81

C 83

D 85

Solution

Correct Answer: Option A

Cp1 = p2 - p1 , 
Cp2 = p3 - p2 
..
..
..
Cp23 = p24 - p23
Sum of series = (p2-p1) + (p3-p2) + .....(p23-p22) + (p24-p23)
All terms get cancelled, except p1 = 2 and p24 = 89 
So Sum = -p1 + p24
Sum of series = -2 + 89 = 87

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