help wih sat math q's

Test Preparation
1

<p>1.the avg of the test scores of a class of “p” students is 70, and the avg of the test scores of a class of “n” students is 92. when the scores are combined, the avg is 86. what is the value of p/n?</p>

<li>if x^2 (squared) minus y^2=10 and x+y=5, what is the valye of x-y?</li>
</ol>

<p>TIA!</p>

2

<p>1.</p>

<p>sum of scores for class p/p students = 70
sum of scores for class n/n students = 92
(sum of scores for class n + sum of scores for class p)/(n+p) = 86</p>

<p>sum of scores for class p= 70p
sum of scores for class n= 92n</p>

<p>(70p + 92n)/(n+p) = 86
70p + 92n = 86n + 86p
6n = 16p
3 = 8p/n
3/8 = p/n</p>

<p>That's what I got anyhow. I could be wrong</p>

<ol>
<li>x^2 - y^2 = 10</li>
</ol>

<p>(x+y)(x-y) = 10 <-- (difference of squares)</p>

<p>if (x+y) = 5</p>

<p>5(x-y) = 10
(x-y) = 2</p>