Question 1203352
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We can organize the data into a two-way table.
<table border = "1" cellpadding = "5"><tr><td></td><td>Men</td><td>Women</td><td>Total</td></tr><tr><td>In favor</td><td>A</td><td>B</td><td>C</td></tr><tr><td>Opposed</td><td>280</td><td>320</td><td>D</td></tr><tr><td>Total</td><td>500</td><td>500</td><td>1000</td></tr></table>
I'll let the student fill in the gaps.


Hopefully it is fairly obvious that we have the following equations when looking at each column separately
A+280 = 500
B+320 = 500
C+D = 1000


We also have these three equations when focusing on the rows separately
A+B = C
280+320 = D
500+500 = 1000


Another equation that can be formed is this
A+B+280+320 = 1000
which represents adding up the inner 2x2 block of values to get the grand total
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