Question

In an A.P. the eighth term is twice the third term The 20th term is 210. Find the sum of first 100 terms.​

Answer 1

Answer:

=>a+(8-1)d=2(a+(3-1)d)

=>a+7d=2(a+2d)

=>a+7d=2a+4d

=>3d=a

=>a=3d

t20=210

=>a+(20-1)d=210

=>a+19d=210

=>3d+19d=210

=>21d=210

=>d=10

thus,a=3*10=30

thus,

s200=n/2(2a+(n-1)d)

=>200/2(2*30+(200-1)10)

=>100(60+1990)

=>100*2050

=>205000(Answer)

Answer 2

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