Just to confirm what Lee has said, this time from a British perspective: 1. No - as Lee has explained. 2, 3, 4, 5. Yes, with regard to UK currency. 'A penny' is the name of small coin. In Britain, this coin is one hundredth of a pound sterling. In the US, it refers to the one cent coin - one hundredth of a dollar. If I am not mistaken, this is the only use of the word 'penny' with regard to US currency. In the US, a penny is an object - a coin worth one cent, just as a quarter is a coin worth twenty-five cents and a nickel is a coin worth five cents. A 'penny' is not a denomination of actual currency in the US - it's just the name of a small coin. The denominations of US currency are dollars and cents. In Britain, however, 'penny' and the plural 'pence' are also denominations of our currency. Just as the US has dollars and cents, the UK has pounds and pence. The term 'pence' refers to currency (prices, values and so on) in the UK. This is why the term 'pence' (as in 50p, fifty-pence piece, and so on) is used to refer to UK currency, but not to US currency. Finally, just one language point: Note that we don't use 'of' following the word 'worth'. The correct construction is 'a coin worth fifty pence', not 'of fifty pence'. I hope that's all clear now!

U.S. speakers do not use the word "pence." U.S. speakers have specific names for the coins in common use: the penny, the nickel (five cents), the dime (ten cents), and the quarter (twenty-five cents). Amounts of money are always named in "dollars and cents." "How much does it cost to do a load of laundry in this laundromat?" "A dollar and seventy-five cents," or "a dollar seventy five." You would not normally use the names of coins to describe an amount of money. You might say "The machine only accepts quarters, so you need to have seven quarters to operate it." It has been over fifty years since I last heard anyone a describe a coin as a "piece." When I was a kid, a coin with a value of $0.50 was in common circulation and was described either as "a fifty-cent piece" or, more commonly, "a half-dollar." No other coins are ever described that way. A dime is not "a ten-cent piece" or "a ten-penny piece." So, an amount of money is described in dollars and cents, and the individual coins we use are pennies, nickels, dimes, and quarters. The half-dollar exists and is legal but is almost never seen. There is an ongoing controversy about our dollar coins, are almost never seen and don't really have common names. Starting in the 1970s there have been innumerable attempts to introduce dollar coins, first the Susan B. Anthony dollar, then the Sacajawea dollar, than the Presidential dollars--and the public has completely rejected them. You never see them, unless you use a vending machine that accepts paper currency and it gives you change in dollar coins... and then you never know what to do with the dollar coins except to use them in other vending machines.

1. How much is it ? It's fifty cents . Will Americans say "It's fifty pence " also? No, we have cents, not pence. 2. If I say " a fifty pence piece " , does it mean there is only one metal coin which is worth of 50 pence ? Yes, but Americans don't have pence, so this would be a fifty-cent piece in the USA. We would probably say coins instead of pieces. 3. If I say " a few fifty-pence pieces " ,does it mean there are several metal coins and each one is worth of 50 pence? Yes. "Fifty-pence should be hyphenated. Americans don't have pence, so this would be a few fifty-cent pieces in the USA. 4.Since there are only 50p/20p/ 10p/5p/2p/1p ,I can only say 50 pence piece/20 pence piece/ 5 pence piece/2 pence piece /1 penny piece to stand for metal coins ,right. No. Americans have half-dollars (50 cents), quarters (25 cents), dimes (10 cents), nickels (5 cents), and pennies (one cent). 5. So I can say 30 pence but I can't say a 30 pence piece since there is no metal coin which is worth of 30 pence ,right ? Correct. In the USA, 30 cents would require a quarter and a nickel; three dimes, six nickels; 30 pennies, etc.