THE RATIO OF 11th TERM TO 8th TERM OF AN A.P IS 2:3. FIND THE RATIO OF THE 5th TERM TO TH21th TERM AND ALSO THE RATIO OF THE SUM OF THE FIRST FIVE TERMS TO THE SUM OF THE FIRST 21 TERMS .

Let *a* and *d* be the first term and common difference of the A.P. respectively.

*n*^{th} term of A.P. *a _{n}*

_{ }=

*a*+ (

*n*– 1)

*d*

Given, *a*_{11} : *a*_{8} = 2 : 3

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