Question

The first term 5 & the last term is 145 .
Find the number of terms if their sum is 600​

Answer 1

$\sf\underline{Answer:}$

The number of terms is 8

$\sf\underline{Explanation:}$

First term (a) = 5

last term (n) = 145

$a_{n} = a + (n - 1)d$

$145 = 5 + (n - 1)d$

$(n - 1)d = 140$

Given, sum of terms is 600

$S_{n} = \frac{n}{2}[2a + (n - 1)d]$

$600 \times 2 = n[2(5) + (n - 1)d]$

$1200 = n[10 + 140]$

$150n = 1200$

$n = \frac{1200}{150} = 8$

The number of terms = 8

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