Write a real world problem that correspond to the equation 10x + 30 = 100?

10x + 30 = 100

Here is a real world problem to demonstrate this.

Mack decides to burn some calories, so he attends a gym. A cost of a gym costs 10 dollars per month, with an addition registration fee of 30 dollars. Mack has spent 100 dollars on the gym so far. How many months has he been participating at the gym?

Let 'x' represent the amount of months spent.

Saturday night after the marshmallows ran out, the counselor

threw 30 cold stones on the campfire, and sent the campers

to bed in their tents.

But several campers noticed that there were still live coals in

the fire. This was a tent situation, and they knew that they

should not leave until it's completely out. So they each

picked up 10 cold stones and they all threw those on the fire

too. Then the fire was really out, so they all went to their tents.

In the morning the same campers who threw 10 stones apiece

onto the fire all got together and went to look at it. It was definitely

stone cold, so they spread it out and counted all the stones in it.

They found that there were exactly 100 stones. How many

campers threw stones on the fire after the counselor left?