Hi

I need a formula for the following word problem.
The cost of a cellphone has increased by 400% over 10 years. Does this correspond to a decrease of 4 times its cost?

What is the question?

if the current cost is $x
then the cost 10 years ago was $x/4

A chemist is using

389
milliliters of a solution of acid and water. If
19.5%
of the solution is acid, how many milliliters of acid are there? Round your answer to the nearest tenth.

To answer this question, we will create a formula and do some calculations.

Let's assume the original cost of the cellphone is 'x'.
According to the problem, the cost of the cellphone has increased by 400% over 10 years.

To find the new cost, we need to calculate the 400% increase on the original cost:
Increase = 400% of x = (400/100) * x = 4 * x

Now, we need to find out if the increase corresponds to a decrease of 4 times its cost.

To do this, we can calculate the difference between the new cost and the original cost:
Difference = New Cost - Original Cost

For the new cost, we found that it is 4 times the original cost:
New Cost = 4 * x

Plugging in the values, we have:
Difference = 4 * x - x = 3 * x

If the difference is 4 times the original cost, then:
Difference = 4 * Original Cost

Comparing the equations, we have:
3 * x = 4 * x

However, since the equation is not valid (3x is not equal to 4x), we can conclude that the cost increase of 400% over 10 years does not correspond to a decrease of 4 times its cost.