Quick Math Help - GreenHybrid

Jason · #1 (**permalink**) 08-07-2005, 11:42 PM

For the mileage database, a small display bug was pointed out. To rectify it, I need to calculate the MPG for the tanks that are logged. It's late and my brain is fried. Can anyone else figure out the equation?

Known: Lifetime MPG, Lifetime Miles, Starting MPG, Starting Miles, Tank Miles
Need: Tank MPG

This may be really easy, but at 1:45 after all I've been doing on this thing... can't think! Thanks.

tbaleno · #2 (**permalink**) 08-08-2005, 12:06 AM

can it be done? how can you ever know tank mpg without knowing tank gallons

You can maybe take a guess at it and assume all tanks had equal gallons. But this tank could be the exception to the rule.

I think you need tank gallons to do this equasion.

Jason · #3 (**permalink**) 08-08-2005, 12:15 AM

Haha. I think not! I'll figure it out tomorrow when I get some more sleep

Trust me, it's possible.

BTW how do you think I calculate lifetime mileage when I never know how many gallons anyone ever uses?

rjbarlow · #4 (**permalink**) 08-08-2005, 02:40 PM

Jason,

If I could to real math.... Never mind. Math was not my subject. I have not had a math class since 10th grade geometry in 1975. I never had Algebra II, or Trig, or Calc, but...

I think what you are talking about can be figured by taking miles for a given tank, divided by total miles, to get a percentage that tank represents of the total miles. Multiply that number by the mpg for that tank, and you get X. Do the equation again for another tank and you get X1, and again for another tank and you get X2, and again for another tank and you get X3.... Add X, X1, X2, X3, etc together, and you get an mpg for the total number of miles entered.

Am I making any sense? It frightens me to think I might be. Don't ask me how I came up with this. I don't know.

Bob

Quote:

Originally Posted by Jason

For the mileage database, a small display bug was pointed out. To rectify it, I need to calculate the MPG for the tanks that are logged. It's late and my brain is fried. Can anyone else figure out the equation?

Known: Lifetime MPG, Lifetime Miles, Starting MPG, Starting Miles, Tank Miles
Need: Tank MPG

This may be really easy, but at 1:45 after all I've been doing on this thing... can't think! Thanks.

rjbarlow · #5 (**permalink**) 08-08-2005, 02:45 PM

Jason,

Isn't this the same formula you use to figure out cumulative mpg for each member? All you need to do for me is use the formula you use now to calculate mpg, but subtract the "at start" numbers from your formula.

Does this make sense?

Bob

Jason · #6 (**permalink**) 08-08-2005, 02:45 PM

Hmm. That requires a loop... a bit code intensive. I'm telling you... there IS a better way! I'll figure it out soon.

Jason · #7 (**permalink**) 08-08-2005, 02:47 PM

If any of you know PHP, maybe this could help. It's the code to calculate lifetime MPG.

Code:

$carQUERY=mysql_query("SELECT tanks, mi_start, mpg_start FROM cars WHERE cid=$cid");
$car=mysql_fetch_array($carQUERY);

// Grab tanks data
$tanks=0;
$tankQUERY=mysql_query("SELECT mi, mpg FROM tanks WHERE cid=$cid AND deleted=0");
while($tank=mysql_fetch_array($tankQUERY)) {
	$tanks_bit=$tanks_bit + ($tank['mi']/$tank['mpg']);
	$mi_tanks=$mi_tanks + $tank['mi'];
	$tanks++;
}

// Define car data
$mi=$car['mi_start']+$mi_tanks;
if($car['mpg_start']>0) {
	$mpg=$mi / ($tanks_bit + ($car['mi_start']/$car['mpg_start']));
} elseif ($mi_tanks>0) {
	$mpg=$mi_tanks / $tanks_bit;
} else {
	$mpg=0;
}

rjbarlow · #8 (**permalink**) 08-08-2005, 02:49 PM

Well, I don't know anything about computer programming either.

You are on your own!

rjbarlow · #9 (**permalink**) 08-08-2005, 02:54 PM

Jason,

Now I am really treading into the unknown, I know NOTHING about computer language or programming. But what if in the third line of the partial quote below you changed ">0" to "=0" as the formula just to calculate the progress since adding tanks? Isn't that the code entry that tells the calculator that the mpg start may be something above 0, as in 23,151 miles in my case?

Bob

Quote:

Originally Posted by Jason

If any of you know PHP, maybe this could help. It's the code to calculate lifetime MPG.

[// Define car data
$mi=$car['mi_start']+$mi_tanks;
if($car['mpg_start']>0) {
$mpg=$mi / ($tanks_bit + ($car['mi_start']/$car['mpg_start']));
} elseif ($mi_tanks>0) {
$mpg=$mi_tanks / $tanks_bit;
} else {
$mpg=0;
}[/code]