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Bader A.

asked • 09/27/18

arithmetic sequence question !!!

Assume that a1,a2,a3,....ak form an arithmetic sequence. If we have a5 + a8 + a11 = 10 , a7 + a10 + a13 = 12  , and ak=11 , the k=      ????
 
 

1 Expert Answer

By:

Mark M. answered • 09/27/18

Tutor
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Mathematics Teacher - NCLB Highly Qualified

Bader A.

K = 31  ????
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09/27/18

Al P.

tutor
Yes, k = 31.
 
For completeness:
The two equations are  3a5+9d = 10   and   3a5+15d = 12   ==>  d=1/3  and  a5=7/3
ak = 11 = a5 + (k-5)d
        11 = 7/3 + (k-5)(1/3)
        33 = 7 + k - 5   —>  k = 31
 
 
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09/28/18

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