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A number in disguise

BrainteasersEasy

Mira thinks of a number. She multiplies it by $3$ and adds $4$ , then repeats the same $2$ steps on the result, and then once more, $3$ rounds in all. The final result is $187$ . What number did she start with?

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Hint

Undo the rounds in reverse order: subtract first, then divide.

Solution

Undoing the last round gives $\frac{187 - 4}{3} = 61$ .
Undoing the middle round gives $\frac{61 - 4}{3} = 19$ .
Undoing the first round gives $\frac{19 - 4}{3} = 5$ , so she started with $5$ .

Answer: $5$

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