**Direct proportions:**

**Formula: y = kx**

y = output

k = constant

x = input

**Characteristics:**

1. As x increases, y increases proportionately.

2. Graph makes a straight line.

3. Line passes through point of origin (0, 0).

4. Line does not cross either axis (no negative numbers).

**Inverse proportions:**

**Formula: y =**

__k__**x**

y = output

k = constant

x = input

**Characteristics:**

1. As x increases, y decreases proportionately.

2. Graph makes a curved line.

3. Line does not pass through point of origin (0, 0).

4. Line does not cross either axis (no negative numbers).