1.

5, 15, 35, 75, 155, _____(a) 215 (b) 305 (c) 315 (d) 265

Answer»

Correct option is : (c) 315

5, 15, 35, 75, 155, ……….. 

5 × 1, 5 × 3, 5 × 7, 5 × 15, 5 × 31, ……………. 

5(21 – 1), 5(22 – 1), 5(23 – 1), 5(24 – 1), 5(25 – 1), ……….. 

So, next number is 5 x (26 – 1) = 5 × 63 = 315



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