Homework help.... How can i remember what the difference in...?

Question

remember the difference between directly proportional and inversely proportional and indirectly. When I see these in question I can not understand the question. Can anyone help me please!?

EX:

In reference to the H & D curve, how are latitude & contrast related?

A. Directly proportional
B. Indirectly propportional
C. Inversely proportional

This is an example of the questions.

Answer 1

I'm not familiar with the term "indirectly proportional". That's probably a "red herring" (a made up answer to confuse you).

I find it easier to remember "inversely" than it is to remember "directly" -- although directly should be more familiar to you.

Inverse proportions are like:

xy = k

For instance, you have 10 pies and 5 students. 10 is k; 5 is x. How many pies will each student get?

5y = 10
y = 2 pies per person

Now, if you only had 2 students:

2y = 10
y = 5 pies per person

So what happens an INVERSE proportion is that when one number goes UP, the other goes DOWN. When a number goes DOWN, the other goes UP.

A DIRECT proportion is exactly the opposite. It looks like:

y = kx

(Notice that DIRECT proportions look just like the equation of a line, y = mx + b, except that b is zero.)

Using a similar example, if you have 5 students (x), and you want each student to have 2 pies (k), then you'd need to make

y = 2(5) = 10 pies

But if you have 10 students (x), and you want each student to have 2 pies (k), you'd need to make

y = 2(10) = 20 pies.

So:

In an INVERSE proportion, when x goes up, y goes down, and vice versa: xy = k or y = k/x

In a DIRECT proportion, when x goes up, y goes up, and vice versa: y = kx

And as far as graphs go...inverse proportions look like this: http://homepage.mac.com/cbakken/proportions/image93.gif and direct proportions look like straight lines.

Answer 2

It would be helpful if you provided us with a homework problem to work on, please.

A. Indirectly proportional - you use division
B. Directly proportional - you use multiplication