Respuesta :

Let the number be x.

double it and add 5
⇒ 2x + 5

The result is 1 less than the number she thought of
⇒ x - 1

Construct the equation to solve for x:
2x + 5 = x - 1 
x + 5 = -1           // Take away x from both sides
x = -6                // Take away 6 from both sides

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Answer : The number Tui first thought of is -6.
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