All of the shoppers in a grocery store are either male or female.

Actually this is a very easy question.

Remember integer constraint is implied because we are talking about people. It can't be 1/2 or 3/4 of a woman. So 1,2,3,4.... Now first one doesn't tell us much. 10 more females than males so what? There could be 2 females and 12 males or 50 females and 60 females. So that's not the answer.

2) doesn't tell us much either because there could be (remember integers) 4 females and 6 males = 40% females. or 8 females and 12 males. 8/20 is 40%. or There could be 40 females and 60 males....

Add them together, has to be 40% females and 10+ males than females. So think of it as a ratio question:

4 females, 6 males = 40% - less than 10
8 females, 12 males -- still less than 10
12 females, 18 males....
16 females, 24 males
20 females and 30 males. BINGO - This satisfies both conditions. 10 more males than females and 40% are females. 20/50 is 40%. So there you have it.

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