the ratio of the 11th form to the 18th term of an AP 2:3 . find the ratio of the 5th term to the 21st term and also the ratio of the sum of the first 21 terms
sinhaankitalko:
what do you mean by ratio of sum of first 21 terms
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a11/a18=2/3
3*a11=2*a18
3*(a+10d)=2*(a+17d)
3a+30d=2a+34d
a=4d
a5/a21=(a+4d)/(a+20d)
=(a+a)/(a+5a) since a=4d
= (2a)/(6a)
=1:3
3*a11=2*a18
3*(a+10d)=2*(a+17d)
3a+30d=2a+34d
a=4d
a5/a21=(a+4d)/(a+20d)
=(a+a)/(a+5a) since a=4d
= (2a)/(6a)
=1:3
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