math
posted by Riana .
t11=19 and t17=61.then what will be S12?
arithmetic series question

a+10d = 19
a+16d = 61
subtract them
6d = 42
d = 7
a + 70 = 19
a = 51
sum(12) = (12/2)(102 + 11(7) ) = 150
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