Question

Antonio has a total of 55 marbles. He has 15 green marbles and 12 red marbles. The rest of the marbles are blue. How many blue marbles does he have?

I know the answer is 28 because 15 and 12 is 27 and the sum of 55 and 27 is 28.

But then the question says:
A student solves this problem by writing an equation. Which strategy could help check the student’s answer?

Check that the sum of the final answer, 12, and 15 is 55.
Check that the difference of 55 and the final answer is 12.
Check that the sum of the final answer, 27 and 15 is 55.
Check that the difference of 55 and the final answer is 15.

This is where I am confused.

Answer 1

it should be the "check the sum of the final awasnser, 27 and 15 is 55

Answer 2

yes, that one. green + red + blue has to be 55

Answer 3

So is the third one saying that 27 was the final answer and you add 15?
Or was it saying that you add the 28 + 27? because if you do than what is the 15 for?
Maybe I am just over thinking it.

Answer 4

No, its saying
final answer + 7 + 15 = 55
for you final answer is 28
so,
28 + 7 + 15 = 55

Answer 5

Oh, okay. Gotcha. Sorry, it's early.

Answer 6

No problem