Question

Find the sums given below : (i) `7+10 1/2+14+dot dot dot+84`(ii) `34+32+30+dot dot dot+10`(iii) `5+(8)+(-11)+dot dot dot+( 230)`

Answer 1

Correct Answer - (i) `1046(1)/(2)` (ii) 286 (iii)-8930 (iv) 420
`(i) a = 7,d = ((21)/(2) - 7) = (7)/(2) "and" I = 84.`
`T_(n) = 84 rArr a + (n-1)d = 84 rArr 7+(n-1) xx (7)/(2) = 84 rArr n = 23.`
`S_(23) = (n)/(2)(a+l) = (23)/(2)(7+84) = 1046(1)/(2).`