Stefan bought 5 posters to add to his collection. a week later half of all his posters were lost during a move. there are now only 15 posters left. with how many posters did he start?

he started with 35 posters

Step-by-step explanation:

Let x represent the number of posters that he started with.

Stefan bought 5 posters to add to his collection. This means that the number of posters at this point is

x+ 5

A week later half of all his posters were lost during a move. This means that the amount of posters that were lost is (x+5)/2

The amount of posters left would be x - (x+5)/2

There are now only 15 posters left. This means that

x - (x+5)/2 = 15

Multiplying through by 2

2x - x - 5 = 30

2x - x = 30 + 5

x = 35

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step-by-step explanation: