How To Calculate 'Cents On The Dollar'?

Pretty easy, if offered .50 on the dollar, (1.00) that is half.  If someone offers you .40 on the dollar, you pay $40 per hundred.  Don't know if you are a gambler or if you might be in debt to a bookie, but that is they way is calculated.  A person I know was offered .50 per $1.00 on credit card debt, then the next day was offered .60 per $1.00.  The .50 was 1/2 off, the .60 was 40% off.
Hope this helps.