find the ratio of their 11th terms, Mathematics

The  ratio of the sum of first n terms of two AP's  is 7n+1:4n+27.  Find the ratio of their 11th  terms .

Ans:    Let a1, a2... and d1, d2 be the I terms are Cd's of two AP's.

Sn of one AP    = 7n+1/4n+27

Sn of II AP 

m/2[2a1 +(n-1)d1]/ m/2 [2a2 +(n-1)d2] = 7n+1/4n+27

 

ð  2a1 +(n-1)d1/ 2a2 +(n-1)d2 = 7n+1/4n +27

ð  We have sub n = 21

ð  2a1 +20d1/2a2 +20d2 = 7 x21 + 1/4(21)+27

ð  A1 +10d1/a2 +10d2 = 148 /111

ð  = 4/3

Posted Date: 4/8/2013 6:00:30 AM | Location : United States







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