Part A
x = some unknown number
2x = doubling that number
2x+11 = adding on eleven
Answer: 2x+11 = 25
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Part B
If we knew what x was, then we can compute 2x+11 using the order of operations PEMDAS. Because x is unknown, we follow PEMDAS in reverse to isolate x.
So we'll undo the addition first by subtracting 11 from both sides. Then we undo the multiplication by dividing both sides by 2.
2x+11 = 25
2x+11-11 = 25-11 ..... subtract 11 from both sides
2x = 14
2x/2 = 14/2 ...... divide both sides by 2
x = 7
The number the person thought of was 7. Double 7 to get 14. Add on eleven to get 14+11 = 25.
Answer: x = 7
