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hi
this kind of problem needs 3 equations...
at the first you we have 3 steps
let's suppose that at the begining there was X apples,then after the first buying Y apples then a person bought Z apples to get at the end 1 apple.
at the first a perosn bought half of the apples and half an apple
so this is the equation to get Y apples :
Y = X - 1/2X - 1/2
just to make it clearer the origin one is
Y = X - (1/2X + 1/2)
now we have to know Z Apples which is written in this equation :
Z = Y - 1/2Y - 1/2
at the end we got 1 apple
so
1 = Z - 1/2Z - 1/2
as you saw we have to get the previous number from subsequent one
so we must now resolve the third equation which will give us :
Z = 3
we replace Z in the second equation by its value so we will get
Y = 7
evatually we give Y its value in the first equation and we will get X which is the original number of apples
X = 15
hope it is correct
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thanks