Question

Multiples of 9 lying between 300 and 700

Answer 1

Here series will be = 306, 315, 324, 333,...........693

So we have the first term a = 306 and d = 9 and last term l = 693

693 = 306 + (n-1)9

77 = 34 + (n-1)

n = 77 - 34 +1

   = 44

Sum = n/2(a+l)

        = 44/2(306+693)

        = 22(999)

        = 21978.


Hope this helps!

Answer 2

HEY THERE!!!

Question;-

Find the sum of all multiples of 9 lying between 300 and 700.

Method of Solution;-

Firstly, find which number lies on sum of all multiples of 9 lying between 300 and 700.

Number which are multiples of 9 lying between 300 and 700 Given Below in the form of Arithmetic Sequence or Progression.

306, 315, 324, 333, ..., 693.

here,
 a = 306, d = (315 - 306) = 9 and l = 693.

Let the number of terms be n.
Then Tn = 693

⇒ a + (n - 1)d = 693

= 306 + (n - 1​) 9 = 693

= 9n = 396

= n = 44

∴ Required sum = n /2(a+l)
                  ‎‎‎‎‎‎‎‎‎= 44/2(306+693)
‎ =22(306+693)
‎
‎ =22(999)
‎
‎ =21978

Hence, sum of all multiples of 9 lying between 300 and 700 = 21,978.

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