Question

Read the word problem below.

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?

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.

Answer 1

Ok well this should be easy,

So, the total amount of marbles is 55 and the amount of green marbles is 15 and red marbles is 12

So I'm just going to make variables so that it would be easier,
\[55t\\ 15g\\ 12r\] \[t=total\\ g=green\ marbles\\ r=red\ marbles\] this is basically saying

Answer 2

```
Total amount of marbles: 55
Amount of Green Marbles: 15
Amount of Red Marbles: 12
```
So that's the information we need to know.
We need to find the amount of blue marbles.
So from that we can write out that
\[55=12+15+(the\ amount\ of\ blue\ marbles)\]

Answer 3

Sp the amount of blue marbles is still unknown and to find it we would have to work backwards. When I say work backwards I mean we have to subtract instead of add.
but first we have to identify the amount of marbles there are that aren't blue, it doesn't matter what color those ones are we just need the number. So what we will be doing it adding the amount of marbles we already know. So\[15+12=27\]So we have 27 marbles that aren't blue, so now the remaining one's have to be blue since he only had blue red and green. So now we have to do the subtracting I was talking about before, \[55-27=28\]

Answer 4

Overall, it would be 55=15+12+28