will this work for Ford Mustang 2011

Yes, I just programmed them (and my old, broken fob) on my 2005 Mustang and they are clear about what years are compatible. It took all of 20 seconds to program the fobs and they all work great.

Will these work for a1998 ford contour?

No, but the company does make a set that does. If you type 1998 Ford Contour key fob into the amazon search bar it will show you the options for your car.

I bought a used ford focus has power locks but did not come with a remote will I be able to use this with my car.

I bought a used 2005 Ford Focus with only one key and one fob. I bought this set of fobs and when they came, I tried using the instructions Di posted on 12/11/2015 as an answer to the question. Turning key to start position 8 times did not work but 4 times did. You might want to go by the instruction that come with the fobs...LOL!! I now have 2 working fobs for my car. Now, to find a new key.

Manufacturer	KeylessOption
Brand	KeylessOption
Product Dimensions	5.08 x 1.91 x 10.16 cm; 50 g
Batteries	1 CR2032 batteries required.
Item model number	KPT1370
Is Discontinued By Manufacturer	No
Item Dimensions L x W x H	5.1 x 1.9 x 10.2 cm
Color	Black
Item Weight	50 g

(キーレスオプション)KeylessOption 交換用4ボタンキーレスエントリーリモートコントロールキーフォブ 2個セット ブラック KPT1370

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(キーレスオプション)KeylessOption 交換用4ボタンキーレスエントリーリモートコントロールキーフォブ 2個セットブラック KPT1370