46.
If Sn denote the sum of the first n terms of an A.P. If S2n = 3Sn , then S3n : Sn is equal to

47.
Sum of n terms of the series $$\sqrt 2 $$  $$ + $$  $$\sqrt 8 $$  $$ + $$  $$\sqrt {18} $$  $$ + $$  $$\sqrt {32} $$  $$ + $$  ....... is

48.
If the sums of n terms of two arithmetic progressions are in the ration $$\frac{{3n + 5}}{{5n + 7}},$$   then their nth terms are in the ration

50.
If 18th and 11th term of an A.P. are in the ratio 3 : 2, then its 21st and 5th terms are in the ratio

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