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- Re: I need some math assist....

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08-20-2013 03:39 AM

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

12/2014: 750+

3/2017 780+

5/2017 800+

12/2014: 750+

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08-20-2013 03:57 AM

Right 3.2883 or $3.29

Discover IT $17k / US Bank Ace (VSig) $13.5K / US Bank Cash+ (VSig) $13.5k

Sam's Mastercard $10.9k / Walmart Mastercard $8k / Blispay $7.5k PayPal Ex MC $6.1k

CareCredit $5k / Husq $5k / Cap1 QS $4.5k / Barclay Ring $4.5k / Citi DC (WMC) $7.1k

Gardening Date 7/01/16 / MyFico 08: EQ 801 / TU 777 / EX 771 / 01/03/17

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08-20-2013 05:49 AM

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

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08-20-2013 06:32 AM

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.

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08-20-2013 06:35 AM

+1

Discover IT $17k / US Bank Ace (VSig) $13.5K / US Bank Cash+ (VSig) $13.5k

Sam's Mastercard $10.9k / Walmart Mastercard $8k / Blispay $7.5k PayPal Ex MC $6.1k

CareCredit $5k / Husq $5k / Cap1 QS $4.5k / Barclay Ring $4.5k / Citi DC (WMC) $7.1k

Gardening Date 7/01/16 / MyFico 08: EQ 801 / TU 777 / EX 771 / 01/03/17

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08-20-2013 05:22 PM

You all rock - thanks!

5/2012: 560 credit scores across the board

12/2014: 750+

3/2017 780+

5/2017 800+

12/2014: 750+

3/2017 780+

5/2017 800+

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08-20-2013 05:28 PM

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

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08-20-2013 05:40 PM

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?

Before you app think...

Have you done your research of the CC?

Does it fit your spending?

Do you have a plan for the bonus w/o going into debt?

Can you afford the AF?

Do you know the cards benefits? Is it worth the HP?

Have you done your research of the CC?

Does it fit your spending?

Do you have a plan for the bonus w/o going into debt?

Can you afford the AF?

Do you know the cards benefits? Is it worth the HP?

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08-20-2013 08:21 PM

@longtimelurker

Real math. I like your style.

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## Re: I need some math assist....

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08-20-2013 08:31 PM

Dubious wrote:@longtimelurker

Real math. I like your style.

Thanks! But just very basic algebra...

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