Question

find X in this series of sum is 287 :
1,4,7,10...........x = 287 ​

Answer 1

Answer:

The value of X is 40.

Step-by-step explanation:

Let, tn = X

For this series,

:. tn = X = 3n–2

$sum = \frac{n}{2} (t1 + tn)$

by using above formula,

$287 = \frac{n}{2} (1 + 3n - 2)$

$287 = \frac{3n {}^{2} - n}{2}$

by solving this, we get the value of n = 14

put the value of n = 14 in tn= 3n–2

:. tn = X = 40

Hope you will understand.

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