How does the percentage of caffeine in regular coffee compare to the percentage in decaffeinated coffee?!

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This is according to the International Coffee Organization:

The amount of caffeine in a cup of coffee can vary greatly, depending on its origin or the composition of the blend, the method of brewing and the strength of the brew. Instant, or soluble, coffee generally contains less caffeine than roast and ground coffee, but may be consumed in greater volume. Robusta coffees have about twice as much caffeine as arabicas. A 'cup' is usually understood to contain 150 ml (5 oz in the United States) but an espresso may be as small as 40 ml.

The U.S. Food and Drug Administration gives the following ranges for caffeine contents:

(mg per 5 oz cup)
range average

Roast and ground
-drip method 60-180 115
-percolator 40-170 80

Instant coffee 30-120 65

Whatever method of decaffeination is used, the decaffeinated green coffee must contain less than 0.1% caffeine (dry weight basis) to comply with EC regulations. This corresponds to about 3 mg caffeine in a cup of decaffeinated coffee.

http://www.ico.org/caffeine.asp