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

Here's what we know that we can put into an equation.
⇒The number of nickels mutliplied by .05 and the number of dimes multiplied by .1 equal 5.00.
⇒2n=d; that means that the number of nickels times 2 equals the number of dimes.
Let's solve:
We can use substitution with out two equations.
0.05n+0.10d= 5.00
2n=d
We can put the second equation in as the value of n in the first equation.
0.05n+0.10(2n)=5.00
Now solve till d has a value.
0.05n+0.2n=5.00
0.25n=5.00
5.00÷0.25=20=n
There are 20 nickels. If there are 20 nickels, there has to be 40 dimes since he has twice as many dimes as nickels. Let's check this with the other equation.
0.05(20)+0.1(40)
1+4=5
So, there are 20 nickels and 40 dimes.
Tell me if this helps!!