Question

please answer me fast.....

Answer 1

I got and of 7th sum

Answer 2

Answer:

7) 465

8) 65 / 12

Step-by-step explanation:

7) Given that,

a = 10 and d = 3

We know that,

Sn = n / 2 { 2a + ( n - 1 ) d }

S15 = 15 / 2 { 2 *10 + ( 15 - 1) 3 }

= ( 15 * 62) / 2 = 15 * 31

S15 = 465

8) Given that,

AP = 1/6 , 1/4 , 1/3 , .......

So,

a = 1 / 6

And d = 1 / 4 - 1 / 6 = 1 / 12

S10 = 10 / 2 { 2/6 + ( 10 - 1) 1/12 }

= 5 ( 2/6 + 9/ 12)

= 5 ( 13/ 12 )

S10 = 65 / 12