<PRE><B>Question 1202468</B>
Calculate the sum between and including the terms t16 and t53 of an arithmetic sequence with first term 543 and common difference  -  12.

a= 543
d= 12

Sn = n/2(2a+(n-1)d

Sum of 16 terms

S16 = 16/2(2*(543)+15*12) =10128

Sum of 53 terms

S53 = 53/2(2*543+52*12) =45315

Find the difference between them

t16 = a+15d

t16= 543+15*12=723

t53 = a+52d

=543+52*12 =1167

Sum including these terms t16 and t53
Think it over
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