What do you define as proportionality it refers to a relationship; now this relationship is defined as either directly proportional or inversely proportional.
Now take case A; y is directly proportional to X - we say y varies as X varies in a progressive or retrogressive manner .The 7 serves as a constant which comes in handy when ever an equality is been introduced to an item of proportionality.
Also in case B,
As X changes y changes- x is the sole determinant of this y and hence as X increases or decreases y does so likewise.
D ; y decreases as X increases and y increases as X decrease; here the relationship of proportionality is converse . When the graph of D is plotted using any testing values we see that the graph cuts the y axis at 5 and the X axis at 5.
. ALL of the beverages at The Zest Nest ARE LIKELY to contain 46 grams of sugar or less, but NONE of the beverages at Jim's juice joint ARE LIKELY to contain LESS THAN 46 grams of sugar.
