If x and y are directly proportional and y = 10 when x = -5, what is the value of x when y = 6?
Read the question carefully. What kind of relationship does x have with y?
Identify the bottom line. You are looking for a value of x.
Assess your options. Please do not try to draw a coordinate grid for this type of problem! There is a very simple formula that you can use to determine direct variation. It is y = kx. The variable k represents a constant number. All you need to do is plug in your first values for y and x to determine k, which controls the relationship between x and y. Then use that value for k to find the next value for x.
Attack the problem. Once you have a plan of attack, use it! The first pair of numbers that you are given is y = 10 and x = -5. Plug these numbers into your formula and solve for k.
y = kx
10 = -5k
-2 = k
Now you have the number that controls the relationship between x and y. Use that value for k to find x when y = 6.
y = kx
6 = -2x
-3 = x
Loop back. You solved for your bottom line, so all you need to do is select your answer!
The correct answer is (C).
This is a medium level question.