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If 1/5 : 1/N = 1/N : 1/1.25, then the value of N is ?

1. 1.25
2. 1.5
3. 2.5
4. 2.25

Correct Option: C

Given 1/5 : 1/N = 1/N : 1/1.25
⇒ 1/5 x 1/1.25 = 1/N x 1/N
⇒ N² = 5 x 1.25 = 6.25
∴ N = 2.5