There are 27 amendments. All the amendments are neither formal or informal. If an amendment has not gone through the process laid out in the constitution it is not an amendment.
The UK doesn't have a written constitution.
Twenty eight
I keep a copy of the Constitution of the United States of America and the Declaration of Independence on hand by my computer at all times. A footnote prior to the Bill of Rights (the first ten amendments) reads: "On September 25, 1789, Congress transmitted to the state legislatures twelve proposed amendments, two of which, having to do with Congressional representation and Congressional pay, were not adopted. The remaining ten amendments became the Bill of Rights. The amendment concerning Congressional pay was ratified on May 7, 1992, becoming the Twenty-seventh Amendment to the Constitution." The 6th Amendment, concerniing the right to a speedy and public trail by an impartial jury, was, therefore, part of the original Constitution being debated by the "Founding Fathers" of this land. I am constantly being amazed at the intelligence, the foresight, the all-around brilliance of our ancestors. When I compare them with today's political leaders, I find today's leaders sadly lacking and lagging behind those ancestors!
If you mean the Bill of Rights (the first ten amendments of the US constitution), then while there's been a certain amount of infringement upon some of them, all of them are still "in use." In fact, only one amendment is no longer "in use": the 18th amendment (which was repealed by the 21st).
- None they are all important. - There are some amendments that have lost their relevance over time. The Third Amendment, for example, prohibits soldiers from being quartered in a private home without the consent of the owner. If this amendment were removed today, probably nobody would even notice the difference.
The issue of state's rights is still debated by historians and polititians today. The issue of slavery however is not a factor. Slavery was abolished in the US when the 13th Amendment to the US Constitution was adopted.
amendments 13-16
Yup they sure can. There have been several amendments proposed that were not ratified in the past several decades. The most recent of these was sometime in the 70s. It was an amendment that proposed giving Washington D.C. the same voting rights as the states, including representation in Congress.
The United States Constitution has 27 Amendments as of year 2010.
congress
all of them