If for an A.P. 5 = 10 = 51, then what is the value of 15 ?If for an A.P. 5 = 10 = 51, then what is the value of 15 ?
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Given 5th term and 10th term of an AP are 26 and 51 respectively.
a+4d=26
a+9d=51
Solving the above equations, we get
−25=−5d
⟹d=5
Plugging in d = 5 in either of above two equations, we get
26=a+4(5)
⟹26=a+20
⟹a=6
To find the 15th term,
t
15
=a+(n−1)d
⟹t
15
=6+5(15−1)
⟹t
15
=76.
The 15th term is 76.
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