Someone help me with this math question from the blue book!!

Test Preparation SAT Preparation
1

<p>okay, here it is:
Blue book page 746 number 11:</p>

<p>(There’s a table)</p>

<p>RATINGS OF CAR ENGINE OIL</p>

<p>Rating : Relative speed of flow</p>

<p>10W : Half as fast as 5W oil
15W : " " " " 10W oil
20W : " " " " 15W oil</p>

<p>according to the table above, car engine oil with oil rating 5W flow how many times as fast as car engine oil with a rating of 20W?</p>

<p>A) 2
B) 4
C) 8
D) 16
E) 32</p>

<p>Please help me with this one. You know, I really think they should put the explanations in the blue book.</p>

2

<p>The answer is C. </p>

<p>Because each rating flows half as fast as its previous rating (e.g., 15W is half 10W), it follows that each rating flows twice as fast as its subsequent rating (e.g., 15W is twice 20W). Therefore, following the indicated pattern, 10W flows four times as fast as 20W (2x2). Because the question asks for the oil with a rating of 5W, and the independent variable increments are equal (increasing by fives), it follows that the car engine oil with rating of 5W flows 2x2x2=8 (or 2^3) times as fast as that of 20W. (Forgive the wordiness!)</p>

3

<p>ok, the answer to this problem is c. first, you need to set up a chart like the one above but list the 5W also:
5W
10W
15W
20W
then since every oil after 5W keeps getting cut down in speed by half, you can make up numbers to see the pattern better. I would just start with the speed of 1 for 20W and go backwards by doubling the speed for each following oil so you get:
5W-8
10W-4
15W-2
20W-1
by starting backwards and making 20W “1” speed, the speeds are easily comparable and it is seen that the 5W oil is 8 times faster than 20W (8/1 =8).
hope this helped!</p>