There are 250 bricks used to build a wall that is 20 feet high. How many bricks will be used to build a wall that is 30 feet high?

Hint: In this problem, we are given that there are 250 bricks used to build a wall that is 20 feet high and we have to find the number of bricks that will be used to build a wall that is 30 feet high. Here we can see that the given data is based on direct comparison between two different quantities. We can now assume that the given problem is an example of direct proportion, as if the number of bricks increases, the height of the wall increases. We can write it in mathematical form to get the answer.

Complete step by step answer:
We are given that there are 250 bricks used to build a wall that is 20 feet high, we can write it as
\[\Rightarrow \dfrac{250}{20}\]
We have to find the number of bricks used to build a wall that is 30 feet high.
We can assume x as the unknown number of bricks.
We can now write it as,
\[\Rightarrow \dfrac{x}{30}\]
We know that the given problem is an example of direct proportion as if the number of brick increases, the height of the wall increases, we can now write it as,
\[\Rightarrow \dfrac{250}{20}=\dfrac{x}{30}\]
We can now solve the above step, we get
\[\Rightarrow x=30\times \dfrac{250}{20}=375\]

Therefore, 375 bricks are used to build 30 feet high walls.

Note: Students make mistakes while comparing the given data, as the given data is based on direct comparison between two different quantities. We should also remember that direct proportion is nothing but, if a quantity of one object increases, then the quantity of its relating result also increases.