Question

read this word problem. kayla began a science experiment with 18 grams of an unknown solid. during the experiment, the change in the mass of the solid was -7 grams. what was the mass of the solid at the end of the experiment? to solve the problem, edna subtracted 18 - (-7) and came up with an answer of 25 grams. is edna correct? why or why not? yes, edna is correct. no. the answer should have been -25 grams, not 25 grams, because the mass of the solid decreased. no. edna should have added 18 + (-7) because she needed to add the initial mass and the change in mass.

Explanation:

Step1: Identify the correct operation

The initial mass is 18 grams and the change in mass is - 7 grams. To find the final mass, we add the initial mass and the change in mass, so the operation should be $18+(-7)$.

Step2: Analyze Edna's operation

Edna did $18-(-7)$. Subtracting a negative is equivalent to adding a positive, so $18 - (-7)=18 + 7=25$, but this is the wrong operation for this problem.

Answer:

No. Edna should have added $18+(-7)$ because she needed to add the initial mass and the change in mass.