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12.Practice.Tests.for.the.SAT_2015-2016_1128p

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1094<br />

1 1 2 Practice <strong>Tests</strong> <strong>for</strong> <strong>the</strong> <strong>SAT</strong><br />

Practice Test Twelve Answers and Explanations<br />

10. B<br />

Difficulty: Medium<br />

Strategic Advice: The time difference between Littleville<br />

and Williamshire is 5 hours, with Williamshire time being 5<br />

hours later than Littleville time.<br />

Getting to <strong>the</strong> Answer:<br />

If <strong>the</strong> first satellite reaches Williamshire at 6 PM, <strong>the</strong>n it is<br />

1 PM in Littleville, so <strong>the</strong> trip took 6 hours. If <strong>the</strong> second<br />

satellite is in Williamshire at noon and also takes 6 hours,<br />

<strong>the</strong>n it reaches Littleville at 6 PM Williamshire time, or 1 PM<br />

Littleville time.<br />

11. c<br />

Difficulty: Medium<br />

Strategic Advice: The volume V of a sphere is related to its<br />

radius r by <strong>the</strong> equation V = % w3. The original sphere had a<br />

radius of 2 inches. The new sphere has a radius of 2 + 4 =<br />

6 inches. To find how many times greater <strong>the</strong> volume of <strong>the</strong><br />

new sphere is, divide <strong>the</strong> volume of <strong>the</strong> new sphere by <strong>the</strong><br />

volume of <strong>the</strong> old sphere.<br />

Getting to <strong>the</strong> Answer:<br />

Since volume = % w3, this equals<br />

..1 n63<br />

3<br />

..1 n23<br />

3<br />

63<br />

= p-<br />

= 216<br />

-8-<br />

6 cubed is 216, and 2 cubed is 8. Reducing <strong>the</strong> fraction<br />

makes it equal to 27.<br />

12. D<br />

Difficulty: Medium<br />

Strategic Advice: The graph of a function crosses <strong>the</strong> x-axis<br />

when <strong>the</strong> value of <strong>the</strong> function equals zero. Find <strong>the</strong> values<br />

of t at which g(t) = 0 by solving <strong>the</strong> equation t2 - 4 = 0. You<br />

could also Backsolve this problem, plugging each possible<br />

value of t into <strong>the</strong> function to see which ones give a value of 0.<br />

Getting to <strong>the</strong> Answer:<br />

t2 -4=0<br />

(t - 2)(t + 2) = 0<br />

t= 2 or -2<br />

13. D<br />

Difficulty: Medium<br />

Strategic Advice: When working with exponents, convert<br />

<strong>the</strong> values to <strong>the</strong> same base. Then you can concentrate<br />

solely on <strong>the</strong> exponents. If you have trouble working with<br />

exponents, you can Backsolve.<br />

Getting to <strong>the</strong> Answer:<br />

22x- 3 = 8<br />

22x- 3 = 23<br />

Now set <strong>the</strong> exponents equal to each o<strong>the</strong>r:<br />

14. A<br />

2x -3=3<br />

2x =6<br />

X = 3<br />

Difficulty: Medium<br />

Strategic Advice: Since <strong>the</strong> populations vary inversely,<br />

<strong>the</strong>y can be described by <strong>the</strong> equation B = *· where k is a<br />

constant. Use <strong>the</strong> given values of A and B (<strong>the</strong> population<br />

of each species) to find k, <strong>the</strong>n use k to calculate <strong>the</strong><br />

population of species B.<br />

Getting to <strong>the</strong> Answer:<br />

k<br />

500 = 1,000<br />

15. c<br />

500,000 =k<br />

Difficulty: High<br />

B = 500,000 500 = 250<br />

2,000 2<br />

Strategic Advice: In a substitution problem like this, look <strong>for</strong><br />

<strong>the</strong> common term that will help you express one equation<br />

in terms of ano<strong>the</strong>r. Substitute carefully!<br />

Getting to <strong>the</strong> Answer:<br />

Start with <strong>the</strong> smallest equation. Express it in terms of c.<br />

b=-c+4<br />

-b +4=c<br />

Substitute this into <strong>the</strong> o<strong>the</strong>r equation:<br />

a= 3(2c2 + 3c + 4)<br />

a= 3[2(-b + 4)2 + 3(-b + 4) + 4]<br />

a= 3(2(b2 - Sb + 16) + -3b + 12 + 4]

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