SAT Question of the Day 23 Nov 2012

If 24 over 15 = 4 over n, what is the value of 4 times n?

A.     6

B.     10

C.     12

D.     30

E.     60

 

This is a ratio problem. What do we know?

We know that 24 to 15 (24:15) is equal to 4 to n (4:n)

What are we looking for? What is 4 times n or 4n.

Several ways to find:

4 to n is the same as 16 to 4n (expand both top and bottom by 4).

24 to 15 has a common factor of 3 – it is the same as 8 to 5

We can rewrite as 8/5=16/(4n)

Cross multiplying gives:

8 times (4n) = 16 times 5

Divide both sides by 8

(4n)= 16*5/8 or 16/8 * 5 = 2*5 = 10

Another way find the value of n first and then multiply by 4.

The third option is to plug in, but in this case since we have n in the equation and (4n) as the answer it is not as an appealing option as in other questions.

 

Note that the answer on the SAT website follows a correct calculation but marked the wrong answer as the correct one. Don’t be alarmed – this only shows there are humans on the other side of the exam !

 

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