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  • Which term of the AP 3,15,27,39,...will be 120 more than its 21st term?        

Which term of the AP 3,15,27,39,...will be 120 more than its 21st term?

 

 
 
 
 
 

Answers (1)

3,15,27,39,...(given)

We know a_n=a+(n-1)d   (for an AP).....(1)

For a_{21},

a=3

d=12

n=21

a_{21}=3+(21-1)12

a_{21}=3+240

a_{21}=243

Lets assume the term l which is 120 more than a_{21}

So value of l = 243+120=363

Putting the VALUE IN EQUATION (1)

363=3+(n-1)12

363=3+12n-12

363=12n-9

12n=372

n=31

The required number of the term is 31st.

Posted by

Safeer PP

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