Question

if the first term of an AP is 5 ,last term is 45 and the sum is 400 find the number of terms​

Answer 1

Answer:

first term = a = 5

last term = l = 45

Sn = sum = 400

since last term is given we can use the formula $S_{n}$ $=$ $\frac{n}{2}$ $(a+l)$

Putting the values in the formula

$400=\frac{n}{2} (5+45)$

$400 = \frac{n}{2}$ × $50$

$\frac{400 * 2}{50} =n$

$8 * 2=n$

$16=n$

Therefore number of terms = 16

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