In the first column what is X? Tough one if you think hard!
Answer: I thought this was easy! X is the world population in billion.
X
|
Year
|
1
|
1804
|
2
|
1927
|
3
|
1960
|
4
|
1974
|
5
|
1987
|
6
|
1999
|
7
|
2011
|
World Population Milestones(In Billions)
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