Question

Find the sum of the series 3+7+11+.....to 10 terms

Answer 1

As first term (a) = 3
Common difference (d) = 7-3 = 4
Number of terms(n) = 10
aSum = n/2[2a + (n-1)d]
Subsitute the values
aSum = 10/2[2x3 + (10-1)4]
= 5(6 + 36)
= 5x42
= 210

Answer 2

Answer:

210

Step-by-step explanation:

AP : 3, 7, 11,....., to 10 terms.

Here, we have ;

First term (a) = 3

Number of terms (n) = 10

Difference (d) = 7 - 3 = 4

Sum of n terms is given by formula :

$\bf S_n = \frac{n}{2}[2a +(n-1)d] \\ \\ \bf S_{10} = \frac{10}{2}[2 \times 3+(10-1)4] \\ \\ \bf S_{10} = 5 [6 + 9 \times 4] \\ \\ \bf S_{10}= 5[6 + 36] \\ \\ \bf S_{10}= 5 \times 42 \\ \\ \red{\boxed{\bf S_{10} = 210}}$

Hence, the sum of the given AP is 210.