Answers:
- Box 1: -1
- Box 2: -1
- Box 3: 3
- Box 4: 3
- Box 5: 3
See the diagram below.
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Explanation:
Let's say we replaced 3x with y for now.
3x+1 is the same as y+1
So we have y+1 = 10
To isolate y, we undo the addition and subtract 1 from both sides.
That means -1 will go in the first two boxes.
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After that step is done, we have y = 9 which is the same as 3x = 9 after replacing y with 3x.
3x means "3 times x".
To undo the multiplication, we divide both sides by 3.
Therefore, boxes 3 and 4 will have "3" each.
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Box 5 has 3 as well because 9/3 = 3.
The final answer is x = 3.
As a check,
3x+1 = 10
3*3+1 = 10
9+1 = 10
10 = 10
It works out.
Refer to the diagram below.
