multiple ratio to whole number fraction conversions

I am using Excel 2003.

The situation:
I have instructor to student ratios of 1:36; 1:18; 1:9; 1:4; 1:2; 1:1.

My course requires a total amount of man-hours to be utilized, regardless of the ratio.

All classes going through the course have 36 students.
So, for 1 hour of time spent at a ratio of 1:36 there is only one man hour spent. In 1 hour of time spent at a ratio of 1:18 there are two man hours spent. In 1 hour spent at a ratio of 1:1 there are 36 man hours spent; and so on and so on.

Something else that makes this tricky is that every hour is actually only 50 minutes.

What I need is a way to automatically convert multiple hours of one ratio to the proper amount of hours in another ratio.

Example:
I need Excel to convert 5 hours of 1:18 time to 1:4 time. I need it to look and see that 5 hours at 1:18 is 10 man hours then convert those hours to 1:4man hours, which is 22.5 man hours (I think).

Something else that makes this tricky is that every hour is actually only 50 minutes. so after it gets the 22.5 hours (60 minute hours) I need it to convert that to 50 minute hours.

Jeez I hope this made any sense.

How do I make excel do this?

if (C3=I2) and (E3=J1) then (D3*J2)

I think if I could make that happen, I could repeat the process for all possible conditions to get the conversions I want.

I have attached the sheet i am working off of, I think.

In cells C3 and E3 I have drop down boxes that allow a choice of any ratio I use.

In cell D3 I want to be able to put the origianl amount of time alotted to the first ratio.

Then in cell F3 I want the time conversion to pop up.

The table to the right is all the 1 for 1 ratio exchanges.

Example:
I want to choose the current ratio from C3 drop down, let's say 1:18.
Then I want to type in how much time is currently alotted to an event at the original ratio, let's say 100. (As in 100 minutes alloted to a 1:18 ratio)

Then in cell E3 I want to to choose the ratio I am converting to, let's say 1:4.

Then I want cell F3 to automatically show the conversion. In this case it should turn out to be, 22 minutes.

So it should look like

Ratio to convert from---input time---Ratio to convert to---output time

1:18---100---1:4---22


Now this might seem pretty easy to just do the math, but there are much larger numbers at play and this is done very often.

I want to be able to input any amount of time and switch back and forth between different ratios and get all the different time conversions.

That is awesome.
Is there a better name to give this posting to help with people searching for the same thing.