1.

If `a_1,a_2,...`are in A.P. and `a_1+a_5+a_10+a_15+a_20+a_24=225` then `a_1+a_2+a_3+....a_23+a_24` isA. 909B. 75C. 750D. 900

Answer» Correct Answer - D
We have,
`a_(1)+a_(5)+a_(15)+a_(20)+a_(24)=225`
`rArr" "(a_(1)+a_(24))+(a_(5)+a_(20))+(a_(10)+a_(24))=225`
`rArr" "3(a_(1)+a_(24))=225rArra_(1)+a_(24)=75`
`:." "a_(1)+a_(2)+a_(3)+ . . .+a_(24)=(24)/(2)(a_(1)+a_(24))=12xx75=900`


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