An exponential function is written as y = ab^{x} where a is the initial amount, b is the common growth factor/decay factor and x is the number of years.

So, if the initial amount was 800,000 the equation to represent this would be

c(y) = 800,000 \cdot \Big(\frac{1}{2}\Big)^{y} where y is the time in years.

1.If you want to write a table

At year 0, c(0) = 800,000 \cdot \Big(\frac{1}{2}\Big)^{0} = 800,000 copies.

At year 1, c(1) = 800,000 \cdot \Big(\frac{1}{2}\Big)^{1}= 400,000 copies.

At year 2, c(2) = 800,000 \cdot \Big(\frac{1}{2}\Big)^{2} = 200,000 copies.

At year 3, c(3) = 800,000 \cdot \Big(\frac{1}{2}\Big)^{3} = 100,000 copies.

When the number of years is y, c(y) = 800,000 \cdot \Big(\frac{1}{2}\Big)^{y}

2.Just plug in y = 6 if you want the number of copies sold at year 6, to get

c(t) = 800,000 \cdot \Big(\frac{1}{2}\Big)^{6} = 12,500 copies.

I found an answer from math.stackexchange.com

Probability of winning a prize in a raffle - Mathematics Stack Exchange

Now we are going **to** compute the exact answer without **any** assumptions. There
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not win a prize if those 40 tickets are drawn **from** the 1590 tickets that you did not
buy. ... Imagine that the prize **numbers** are drawn and announced one at a time.

For more information, see Probability of winning a prize in a raffle - Mathematics Stack Exchange

I found an answer from www.scientificamerican.com

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Jul 20, 2016 **...** Jim Papadopoulos spent a whole academic **year** at Oregon before starting at MIT
. He did not **write to** bike companies asking for work until the 1990s. ... He has
actually **published** three first-author papers, but just one related **to** bicycle ... in
Corvallis, Oregon, with a gift for **numbers** and a home life in tatters.

For more information, see The Bicycle Problem That Nearly Broke Mathematics - Scientific ...