SSC CGL 2020 PYQ — Question 3

The correct answer is option 2 i.e. $\frac{5}{39}$

⇒ $\frac{1}{15}$+$\frac{1}{35}$+$\frac{1}{63}$+$\frac{1}{99}$+$\frac{1}{143}$

15 = 3 × 5

35 = 5 × 7

63 = 9 × 7

99 = 9 × 11

143 = 13 × 11

= (1/15 + 1/35) + (1/63 + 1/99 + 1/143)

= (7+3)/(5 × 3 × 7) + (143 + 91 + 63)/(9 × 7 × 11 × 13)

= 2/(3 × 7) + 3/(7 × 13)

= (26 + 9)/(3 × 7 × 13) = 5/39.