Reply
Valued Contributor
Posts: 2,978
Registered: ‎02-09-2012
0

I need some math assist....

Seems here in Florida that all of the gas stations want you to use their Card (or cash) or pay $0.06/gal more.

 

But using my Costco TE gets me 3% CB, which was a savings of $0.10/gal.  So if using their card gets the gas from $3.39/gal to $3.33/gal - then using the TE, would get it down to $3.29, right?

 

Or did I forget to carry a 1?

5/2012: 560 credit scores across the board and $500 secured CC
12/2014: 750+ scores across the board and $80k in revolving credit

Get those baddies removed!!!
Mega Contributor
Posts: 16,663
Registered: ‎08-08-2011
0

Re: I need some math assist....

Right 3.2883 or $3.29

Super Contributor
Posts: 9,144
Registered: ‎04-22-2013
0

Re: I need some math assist....

In more detail, for when gas prices change, suppose a gallon costs $x

 

Then with your card, the price is (x+0.06)*0.97= 0.97x + 0.0582      (0.97 = 1-3%)

 

 

This is less than x when

 

0.97x + 0.0582 < x

 

0.0582 < 0.03x

 

i,e. when x > $1.94 per gallon, which is probably always.

 

As a check, if gas was $2 per gallon, you would pay 0.97*2.06 = $1.9982, so just a little bit cheaper.

 

 

In fullish glory, price of gas is x, non-cash/our-card surcharge is y, cashback rate is z

 

(1-z)*(x+y) < x

x+y -z*x - z*y < x

 

y(1-z) < z*x

 

i.e. use your card if:

y*(1-z)/z < x

 

Valued Contributor
Posts: 3,874
Registered: ‎06-05-2013
0

Re: I need some math assist....


Repo-ed wrote:

 

But using my Costco TE gets me 3% CB, which was a savings of $0.10/gal.  So if using their card gets the gas from $3.39/gal to $3.33/gal - then using the TE, would get it down to $3.29, right?

 

Or did I forget to carry a 1?


No idea -- I use a calculator as my arithmetic just isn't there any more.

 

$3.39 * 0.97 = $3.2883.

Mega Contributor
Posts: 16,663
Registered: ‎08-08-2011
0

Re: I need some math assist....

+1

Valued Contributor
Posts: 2,978
Registered: ‎02-09-2012
0

Re: I need some math assist....

You all rock - thanks!

5/2012: 560 credit scores across the board and $500 secured CC
12/2014: 750+ scores across the board and $80k in revolving credit

Get those baddies removed!!!
Community Leader
Valued Contributor
Posts: 5,381
Registered: ‎04-30-2013
0

Re: I need some math assist....


longtimelurker wrote:

In more detail, for when gas prices change, suppose a gallon costs $x

 

Then with your card, the price is (x+0.06)*0.97= 0.97x + 0.0582      (0.97 = 1-3%)

 

 

This is less than x when

 

0.97x + 0.0582 < x

 

0.0582 < 0.03x

 

i,e. when x > $1.94 per gallon, which is probably always.

 

As a check, if gas was $2 per gallon, you would pay 0.97*2.06 = $1.9982, so just a little bit cheaper.

 

 

In fullish glory, price of gas is x, non-cash/our-card surcharge is y, cashback rate is z

 

(1-z)*(x+y) < x

x+y -z*x - z*y < x

 

y(1-z) < z*x

 

i.e. use your card if:

y*(1-z)/z < x

 


That hurt my brain




NFCU Flagship $25,000 I AMEX SPG $23,000 I Chase Sapphire Preferred $17,500 I Discover IT $12,000 I
Community Leader
Senior Contributor
Posts: 26,694
Registered: ‎02-07-2013
0

Re: I need some math assist....


longtimelurker wrote:

In more detail, for when gas prices change, suppose a gallon costs $x

 

Then with your card, the price is (x+0.06)*0.97= 0.97x + 0.0582      (0.97 = 1-3%)

 

 

This is less than x when

 

0.97x + 0.0582 < x

 

0.0582 < 0.03x

 

i,e. when x > $1.94 per gallon, which is probably always.

 

As a check, if gas was $2 per gallon, you would pay 0.97*2.06 = $1.9982, so just a little bit cheaper.

 

 

In fullish glory, price of gas is x, non-cash/our-card surcharge is y, cashback rate is z

 

(1-z)*(x+y) < x

x+y -z*x - z*y < x

 

y(1-z) < z*x

 

i.e. use your card if:

y*(1-z)/z < x

 


That's the formula Chase uses for approvals right? :smileylol:

 

"Intelligence plus character--that is the goal of true education"
Last 5 apps 6/13


Frequent Contributor
Posts: 271
Registered: ‎02-10-2013
0

Re: I need some math assist....

@longtimelurker

 

Real math. I like your style. 

Super Contributor
Posts: 9,144
Registered: ‎04-22-2013
0

Re: I need some math assist....


Dubious wrote:

@longtimelurker

 

Real math. I like your style. 


Thanks!  But just very basic algebra...

Copyright ©2001-2015 Fair Isaac Corporation. All rights reserved.   | Terms of Use | Privacy Policy | Sitemap

IMPORTANT INFORMATION: All FICO® Score products made available on myFICO.com include a FICO® Score 8, along with additional FICO® Score versions based on Experian or Equifax data (additional FICO® Score versions based on TransUnion data are not currently available on myFICO.com). Your lender or insurer may use a different FICO® Score than the versions you receive from myFICO, or another type of credit score altogether. Learn more

FICO, myFICO, Score Watch, The score lenders use, and The Score That Matters are trademarks or registered trademarks of Fair Isaac Corporation. Equifax Credit Report is a trademark of Equifax, Inc. and its affiliated companies. Many factors affect your FICO Score and the interest rates you may receive. Fair Isaac is not a credit repair organization as defined under federal or state law, including the Credit Repair Organizations Act. Fair Isaac does not provide "credit repair" services or advice or assistance regarding "rebuilding" or "improving" your credit record, credit history or credit rating. FTC's website on credit.