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in this video we're going to talk about the quantity theory of money which is based on what is known as the equation of exchange and it tries to relate the money supply M so this is some measure of the money supply with the real GDP Y so that is real GDP and the price level P so this is price level and we'll try to make this tangible in a second and then it also introduces this idea of the velocity of money which is a measure of how much that money supply is how quickly is it circulating if there's a dollar out there how many times per year is it actually changing hands velocity of money and the equation of exchange that is used in the quantity theory of money relates these as following and that the money supply times the velocity of money is equal to your price level times your real GDP and we could view this on a per year basis so let's make this a little bit tangible and actually let's try to make it tangible by making velocity tangible let's say we are in a world where we have whatever we're using for M whatever measure of our money supply let's say it says that we have ten billion it's a relatively small economy right over that is our money supply and let's say that our real GDP in this economy this year is going to be a hundred billion one hundred billion I'll just call it per year and let's say the price level and this is usually some type of index this is one point one so one way to think about it if you take your price level times your real GDP so if you take this product right over here that's going to give you your nominal GDP nominal GDP where if this was 1.0 that would be in reference to some year that you consider your base year so this would be your real GDP in terms of that base year and then you would multiply it times this right over here to get your nominal but given this information pause this video and try to figure out what the velocity of money would be for that year well this is relatively straightforward algebra to solve for V we just divide both sides by M and we would get that our velocity of money in this year is equal to our price level times our real GDP divided by our amount of money and so this is going to be equal to we have one point one times one hundred billion one hundred billion dollars per year divided by ten billion dollars divided by ten billion dollars so what is this going to be one point one times 100 is 110 divided by 10 is 11 so we are going to get this is going to be equal to 11 the dollar units would actually cancel out and all you're left with if you tried to look at the units is 11 times per year and so one way of interpreting this is for these numbers your average dollar is going to circulate 11 times per year if this idea still seems too abstract to you think of it this way let's have an extreme economy where we only have two parties and let's assume that our price level is just a simple one in which case our real GDP would be the same as our nominal GDP and let's say that our GDP this year is 100 billion dollars 100 billion dollars per year now let's take an extreme situation where the amount of money that we have is also 100 billion well this would be a world if there's only two people in this economy or maybe this person just pays that person 100 billion dollars in order to get that much worth of output and so every dollar has just switched hand once so the velocity of money in this situation it would be just one time per year but imagine another scenario where instead of M being equal to a hundred billion imagine a situation where m is equal to $1 where there's only $1 there you could still have a GDP of a hundred billion dollars because that $1 could just switch hands a hundred billion times it would happen hat it would have to happen quite rapidly for it to all happen in the year but this person could buy a dollars worth of goods and services from this person and that person buys a dollars worth of goods from that person and it would go back and forth 100 billion times and so in this situation where you still have the same real and actually nominal GDP if your amount of money is 1/100 billion then your velocity would have to be a hundred billion times higher now the folks who like to think about this equation of exchange and the quantity theory of money they're often known as monetarists and monetarists believed that inflation is fundamentally a monetary phenomenon that if you increase the money supply that that's going to lead to increased inflation and if you decrease the money supply that might slow inflation or even result in deflation so if you want to think about inflation in terms of money we could solve for P from this equation so to solve for P we would just divide both sides by our real GDP and so you would get your price level is equal to the amount of money times your velocity times your velocity divided by divided by real GDP and these monetarists will assume that velocity is constant although folks theorize that maybe it's not constant that technology for example might make it a little bit easier to transact which might make velocity increase there could also be a world where just people's mindsets make them want to transact more or less which could change velocity but monetarists tend to assume that this is constant because it frankly allows you to make conclusions from this equation of exchange and monetarists also assume that changes in the money supply will not have an impact on real output in the long run so not impacted impacted by em in the long run well if you assume that these two things are relatively constant well then you will see this direct relationship between your price level and the quantity of money now in practice this is likely to be an oversimplification like most of our economics models for example coming out of the last recession of 2008-2009 the Federal Reserve practiced quantitative easing where they dramatically increased the money supply right over here but we did not see a commensurate dramatic increase in inflation in the price level now some folks could argue that when the Federal Reserve in 2008 dramatically increased the money supply without a dramatic increase in price levels it might have been because the velocity of money went down that people weren't actually transacting with all of that money that was being injected into the system who knows and if you're always able to use velocity is a bit of a fudge factor well then it puts into debate of how useful this might be but needless to say it is an interesting model to at least think about that if the money supply were to increase dramatically and people transact at roughly the same rate but the actual output that the economy is producing isn't changing it makes some level of common sense that maybe that would increase the price level you'd have more money chasing the same output