the first term of an arithmetic sequence is 10 .twenteth term 60.calculate the sum of first 20 terms
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a.t.q .
a=10
a20=60=a+59d
a+59d=60
10+59d=60
59d=50
d=50/59
d=1.18
S20=n/2[a+(n-1)d]
S20 =20/2[10+(20-1)1.18
S20=10[10+(19)1.18]
S20 =10[10+22.42]
S20 =10[32.42]
S20=324.2
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