l 5 + 6 + 7 + 8 +... + 19' का योगफल बराबर है। (1) 150 (3) 180 (2) 170 (4) 190

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1. (3) ( 1+2+3+ldots .+n=frac{n(n+1)}{2} ) ( therefore 5+6+7+ldots .+19 ) ( =(1+2+3+ldots .+19) ) ( (1+2+3+4) ) ( =frac{19(19+1)}{2}-10=180 )

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