Question

If A={8, 10,12,14,16,18,20} find n(A)

Answer 1

Step-by-step explanation:

T  

n

​

=a+(n−1)d

62=8+(n−1)d

54=(n−1)d...(1)

S  

n

​

=  

2

n

​

[2a+(n−1)d]

20=  

2

n

​

[2(8)+(n−1)d]

40=n[16+(n−1)d]

From (1)

40=n[16+54]

40=n(70)

∴n=  

7

4

​