<p>ok so i'm one of those stupid ppl
but i dun really care
anyway here it is
x=the sum of all integers from 1 to 49 inclusive
y=the sum of all even integers 2 to 50 inclusive
z=the sum of all integers from 1 to 48 inclusive
what is the value of x + y - z?
i mean i can sit there and do the math but it's takin too much time
anyone know the short/real way to do it?</p>
<p>Well x-z is equal to 49, because they all have the same integers except for 49, which only x has. Then i guess you just add, 2+4+6+8... You can do that in time. Is it 669?</p>
<p>the answer is 99
I wrote 27 down</p>
<p>This was a problem on the psat this year... you miswrote it here, though, because x is supposed to equal the sum of all odd integers from 1 to 49. With that, it's really a simple problem: x plus y will give all the integers from 1 to 50, while z gives only the integers from 1 to 48, so the answer is 99.</p>
<p>wow u're really smart
and have a really good memory
but i still don't get it
how did you figure out the sum of 1 - 50 so quickly?</p>
<p>n(n+1)/2 = sum(int(0 - n))</p>
<p>No, the idea is that you don't have to add all the numbers from 1-50. Let me restate the problem, because the mistake in the first post might still be causing confusion:</p>
<p>x=the sum of all odd integers from 1 to 49 inclusive
y=the sum of all even integers 2 to 50 inclusive
z=the sum of all integers from 1 to 48 inclusive
what is the value of x + y - z?</p>
<p>How do you solve this? Well, what happens when you add x+y? If you take all the odd numbers from 1 to 49, and all of the even numbers from 2 to 50, you're just going to get <em>all</em> the numbers from 1 to 50. That's x+y (but don't add it together yet!).</p>
<p>Now, you have to subtract this by z. z is the sum of all numbers from 1 to 48. It will cancel out all the numbers from 1 to 50 except 49 and 50. So, x+y-z is just 49+50, or 99.</p>
<p>By the way, I know that it sounds kind of weird that I remember this problem, but I just recall seeing a bunch of people painfully adding numbers in the psat testing room for 5-10 minutes, and thinking that this was strange, since the problem doesn't require any addition beyond 49+50 (unless you don't think about it). It stuck out in my memory.</p>
<p>OMG
seriously u're so smart!
i've been smacking my head on the wall for the whole day and still couldn't figure it out T<em>T
u must gotten like a 800 on the math T</em>T
guess what
i finally realize sat isn't the test of math and english
it's the test of IQ...
anyway thanks a lot~</p>
<p>No problem.</p>