From the graph The year -

1980 - 1981 , 1981 -1982, 1982 -1983 and 1983 - 1984 all of them have total charge at private colleges at least $3,000 more than the total charge at public colleges

i.e. option C
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How to do this in less than a minute?

I am thinking the same, Should I need to add all those values to know the quantities are bigger or not. What is your suggestion rx10 sir?
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We are asked for the diff of atleast \($3000\).

From the graph, it is clear that all the public school expense is above \($1000\) hence for the private it should be atleast \($4000\) - to get \($3000\) difference. So you can easily remove the first \(3\) bars from consideration.

For the next \(3\) bars, the public expense is nearly \($2000\) but for private it is less than \($5000\) so difference of \($3000\) can't be achieved.

Last \(4\) did just that hence the answer.

Hope it is clear now.

Observation is the key here. One can definitely do it in 60-70 seconds.


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Gret response sir rx10