and
18 respectively.
23. The last term of an A.P. is 120. Its first
term and common difference are 20 and
5 respectively. Find the sum of the AP.
24. In an AP the sum of first ten terms is -150
and the sum of its next ten terms is - 550.
Find the AP.
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Answer:
23.last term 120
a=20&d=5
an=a+(n-1)d
therefore,120=20+(n-1)5=120-20=(n-1)5
100/5=(n-1)
20+1=n
21=n.
s21=21/2(20+120)
s21=21/2(140)
s21=21*70=1470.
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