When there is at least one pair of x and y whose ratio is different from the ratios for the others.
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Generally, if y increases as x increases, this is a hint that the quantity is directly proportional, and if y decreases as x increases, the relation might be inversely proportional. However, this is not always the case. x and y are directly proportional if y = kx, where k is a constant. x and y are inversely proportional if y = k/x, k is constant. This is the best way to tell whether the quantities are directly or inversely proportional.
According to the equation [ y = 2x ], 'y' is directly proportional to 'x' .
Two variables, X and Y are said to be in inversely proportional is X*Y - k where k is some non-zero constant. X and Y are said to be directly proportional if X = c*Y where c is some constant.
If a variable (such as y) is directly proportional to another variable (such as x), they both increase and decrease simultaneously. An equation for two directly proportional variables is:y = axIt's sort of like a linear equation, but it always goes through the origin.An example is y = 6x. Notice that it forms a straight line and crosses the origin, and that y and x increase in the same direction.
Insufficient information. What is x when y = 12?