Question

The first and last terms of an AP is 17 and 350 respectively . Find how many terms are there in this AP and find their sum if the common difference is 9​

Answer 1

Answer:

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Answer 2

$\huge\bf\pink{Given:-}$

• a(first term)= 17
• a(first term)= 17l(last term)=350
• a(first term)= 17l(last term)=350d(common difference)=9

$\huge\bf\pink{To\:\: find:-}$

• n(number of terms)=?
• s(sum of n terms)=?

$\large\bf\pink{Solution:-}$

As,

$l = a(n - 1)d$

$350 = 17 + (9 - 1)d$

$350 = 8 + (9n - 9)$

$350 = 8 + 9n$

$n = \frac{342}{9}$

$n = 38$

$\huge\bf\blue{So,\: \:n=38}$

Now,

$s = \frac{n}{2}(a + l)$

$s =\frac{38}{2} (17 + 350)$

$s =19 \times 367$

$s =6973$

$\huge\bf\blue{So,\: \:s=6973}$