Math help?

Test Preparation SAT Preparation
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<p>1) Of 200 families surveyed, 75% have at least one car and 20% of those with cars have more than two cars. If 50 families each have exactly two cars, how many families have exactly one car?
I did 20% of 200 is 40, and it says 50 so I added these and did 200 - 90 which is 110, but that answer is wrong. Its a fill in. Could you guys explain?</p>

<p>2) Chairs ready for every shipment at the Northern Chair factory come down a ramp in a single file. Inspector A checks every 3rd chair, beginning with the third. Inspector B checks every 5th chair, beginning with the fifth. If 98 chairs came down the ramp while both inspectors were working, how many of these chairs were not checked by either of these two inspectors?</p>

<p>I saw an explanation on this forum when I did a search but I still don't understand it.</p>

<h2>So 19 and 32 chairs checked (98/3 and 98/5), so that makes 51 chairs CHECKED. 98 - 51 = 47 not checked? Why is the answer not 47?</h2>

<p>Also, a bit off topic - the SATs are in less than 2 weeks... anyone know how I can brush up some math skills quick? Is Dr. Chung good? I can see if theres an ebook.</p>

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<p>1) .25(200) = 50 with 0 cars
50 with exactly two cars
(.20)(.75)(200) = 30 with more than 2 cars
So 200 - 50 - 50 - 30 = 70 with exactly one car</p>

3

<p>75% of 200 = 150 have at least 1 car.
20% of 150 = 30 families have MORE than 2 cars.
50 families have EXACTLY 2 cars.
50+30 = 80 families have 2 or more cars.
150-80 = 70 families have exactly one car. </p>

<p>19 and 32 is right but you have to know that a bunch of the chairs must’ve been inspected by both inspectors. Namely chairs 15, 30, 45, 60, 75, 90. So we have to subtract that from the total of 51. 51-6 = 45 chairs checked.
98 - 45 = 53 chairs not checked. </p>

<p>Not 100% sure but I think these answers are right</p>

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<p>You guys are so good at this! Thank you both heaps.</p>

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<p>Two more… so sorry!

  1. a rectangular puzzle consist of 9 rows of 7 square pieces each. what fraction of the total number lie on the boundary of the puzzle?</p>

<p>I don’t understand this question at all haha. The answer is 4/9.</p>

<p>2)
What I did was use the slope to find the y intercept and got (0,10) as the coordinate. But the answer is 9, not 10?
<a href=“http://i41.■■■■■■■.com/2ezr01u.png[/url]”>http://i41.■■■■■■■.com/2ezr01u.png&lt;/a&gt;&lt;/p&gt;

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<p>http:// imgur . com/ o5ML2kS
You really have to visualize the first question. You don’t have to draw it out but if you really can’t see it, then by all means go ahead. I simply drew it out so you can get an idea of what the question is asking.
I got the same answer for 2, don’t understand why that’s wrong. Hope someone can clarify!</p>

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<ol>
<li><p>63 squares in total. The squares that don’t lie on a boundary form a 7x5 rectangle, so 35 squares are not on the boundary. 63-35 =28, 28/63 = 4/9.</p></li>
<li><p>Y-intercept is 10.</p></li>
</ol>

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<p>Ohh. Silly me, boundary of the puzzle. I kept reading NOT in the boundary of the puzzle. And yeah, I thought the y intercept was 10. My SAT tutor said it was 9. :-(</p>

<p>Thanks guys! And 5am, thank you so much for taking the time to draw everything out and uploading it! :)</p>