Answer:
3
Step-by-step explanation:
Given that there is a pattern in the placing of marbles on the line
9 marbles on I line
8 on second, 7 on third etc.
We find that this follows an arithmetic sequence with I term = 9 and common difference = -1
Hence marbles on 7th line
=value of 7th term in arithmetic sequence
=a+(n-1)d
Here a= I term =9
n = line to be determined = 7
d = -1
Substitute to get
9+(7-1)(-1)
=3
Hence 3 marbles is the answer.
