Question

solve by trick


find sum without adding 1+3+5+7+9+11+13+15+17+19+21=

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Answer 1

Answer:

using Formula... Sn = n/2(a+l)

where a = first no

l = last no .

n = no of terms.

S11 = 11/2(1+21)= 11/2 ×22 = 121

the answer will be 121.

hope it helps you.... brainliest

Answer 2

Step-by-step explanation:

Hello friend,

This is possible by arithmetic progression.

a=1

d=2

a(n)=19

a+(n-1)d=19

1+(n-1)2=19

n-1=18/2

n=10

S(n)=n[2a+(n-1)d]/2=10[2×1+(10-1)2]/2=5[2+18]=100

So, answer is 100.

hope it helps