Question

1+4+7+10+......+67= what?​

Answer 1

a= 1 d = 4-1 = 3 an = 67

So,an = a+(n-1)d

67 = 1+(n-1)(3)

66 = n-1(3)

22 = n-1

n = 23

Now,Sn = n/2(a+an)

Sn = 23/2(1+67)

Sn = 23/2(68)

Sn = 23×34

Sn = 782

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