Question

Without adding find the sum : a) 1+2+3+4+5+7+9+11 b) 1+2+3+.............+21

Answer 1

Answer:

144

Step-by-step explanation:

Total consecutive odd numbers = 5

Thus n = 5

Therefore sum = n2

= 5*5 = 25

ii)

Total consecutive odd numbers = 10

Thus n = 10

Therefore sum = n*n

= 10*10 = 100

iii)

Total consecutive odd numbers = 12

Thus n = 12

Therefore sum = n*n

= 12*12 = 144

Answer 2

Answer:

a)

here__

a=1, d=1 n= 8

By formula we have

S= n/2[2a(n-1)d]

S= 8/2[2×1(8-1)1]

S= 4×14

S= 56 ans

Answer:

b)

here__

a=1 d=1 L=21

By formula we have

a n = a+(n-1)d

21 = 1 + (n-1)1

n = 21

So by formula

S=n/2(a+l)

S = 21/2(1+21)

S = 21×11

S = 231. ans

solution by Yadav ²