Read this word problem.

Question

When Emmett began his science experiment, he had 20 milliliters of an unknown solution. During the experiment, the change in the volume of the solution was
–
9 milliliters. What was the final volume of the solution?
To solve the problem, Dakota added 20+(
–
9) and came up with an answer of
–
11 milliliters. Is Dakota correct? Why or why not?

Answer 1

To solve the problem, we need to determine the final volume after subtracting the change in volume from the initial volume.

Emmett started with 20 milliliters of the solution, and there was a change of –9 milliliters. This means the volume decreased by 9 milliliters.

The calculation should be:

Final volume = Initial volume + Change in volume
Final volume = 20 milliliters + (–9 milliliters)
Final volume = 20 milliliters – 9 milliliters
Final volume = 11 milliliters

Therefore, the final volume of the solution is 11 milliliters.

Dakota's calculation of 20 + (–9) resulting in –11 milliliters is incorrect because Dakota did not correctly perform the subtraction. Instead of adding, he should have subtracted 9 from 20, which leads to a final volume of 11 milliliters, not –11 milliliters.