[Tutor] oops - resending as plain text

[Jim Mooney]

I accidentally sent as HTML so this is a resend in case that choked
the mailing prog ;')

I was doing a simple training prog to figure monetary change, and
wanted to avoid computer inaccuracy by using only two-decimal input
and not using division or mod where it would cause error. Yet, on a
simple subtraction I got a decimal error instead of a two decimal
result, as per below. What gives?

cost = float(input('How much did the item cost?: '))
paid = float(input('How much did the customer give you?: '))
change = paid - cost

#using 22.89 as cost and 248.76 as paid

twenties = int(change / 20)
if twenties != 0:
  twentiesAmount = 20 * twenties
  change = change - twentiesAmount
  #change is 5.8700000000000045, not 5.87 - how did I get this decimal
error when simply subtracting an integer from what  should be a
  #two-decimal amount?
  print(twenties, ' twenties')
  print(change)

#and so forth for the rest of the prog

Jim Mooney