<p>There was a similar question on the Jan SAT:</p>
<p>If 10 people are in class A and 20 are in Class B, if 6 are in one of them and none are neither,
how many people are in both?</p>
<p>Is it just
10+20-6=24
or
(10+20-6)/2 = 12?</p>
<p>because I think i did the first one and is wrong, but i got the answer right can anyone explain this?</p>
<p>First one.</p>
<p>There are 30 spaces filled total.
6 are unique, meaning 6 people fill up only 1 spot.
The other 24 spaces are filled by people that are in both classes, meaning 12 are unique because each of the 12 takes up 2 spots.</p>
<p>The answer is 12. </p>
<p>Working backwards: 12 are in both, so 24 spaces are filled. 6 are in only one, so 6 spaces are filled. 0 are in neither, so 0 spaces are filled. 24 + 6 = 30 = 10 + 20</p>
<p>The problem with this question is that there are only 10 people in class A, even though 12 people are in both classes. Faulty problem, but theoretically the answer is 12</p>
<p>These are best done working backwards from the answer choices. Takes the least brain power.</p>
<p>Crazybandit is right – the question as written is flawed. Could the original question have said “six who are in both”? That would make more sense…</p>
<p>He probably made the problem up because he didn’t remember the original one, hence “There was a similar question on the Jan SAT:”</p>
<p>and I wouldn’t work backwards on a practice problem. Working backwards only accomplishes what you need for a specific problem–that is, answering the specific question correctly. Getting a practice question correct doesn’t help you if you don’t learn how to do it from scratch. It is like plugging numbers into an equation–you don’t learn anything in the process.</p>
<p>There may be a problem on the SAT that does not allow you to work backwards and that may require a similar process of thinking that you might have missed out on if you took the easy way out in studying.</p>
<p>thx crazybandit for the answer, that is what I thought as the right answer after the test, but I distinctively remembered that I put down 24 because I was in a slight brain freeze and I couldn’t think properly.</p>
<p>However, when I checked my math marks and all my mistakes came for numbers and operations and none was from data, statistics analysis and probability. So I was stumped to know that I got the right answer by putting down 24?</p>
<p>hence the reason for clarification on the question</p>