If the 4th and 7th terms of a G.P. are 24 and 192 respectively , find the sum of 5 terms of this G.P. ​

1 thought on “If the 4th and 7th terms of a G.P. are 24 and 192 respectively , find the sum of 5 terms of this G.P. ​”

1. Answer:

   93

   Step-by-step explanation:

   Tn = ar^(n-1)

   T7 = ar^(7-1) = ar^6

   T4 = ar^(4-1) = ar^3

   T7/T4 = ar^6/ar^3

   192/24 = r^3

   8 = r^3

   r = 2 (cube root of 8 = 2)

   T4 = ar^3

   24 = a(2^3)

   24 = 8a

   a = 24/8

   a = 3

   Sum of first five terms

   Sn = a(r^n – 1)/(r-1)

   Sn = 3(2^5 – 1)/(2-1)

   Sn = 3(32 – 1)/1

   Sn = 3(31)

   Sn = 93

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