Question

without adding find the sum of 1+3+5+7+9+11+13+15+17+19 by using property

Answer 1

tn=19
tn = a + ( n -1 )d
19 = 1 + ( n - 1) 2
19 = 1+ 2n- 2
19 = 2n -1
n =18/2
n= 9
now, S= n/2 ×2a+ (n-1)d
S=9/2×2×1 +(9-1)2
S=9/2×18
S = 9 ×9
S=81
hence, the sum of these numbers is 81.
I hope it helps you!
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