When a number is tripled and then decreased by 6 , the result is 15 . The number is
(A) 8
(B) 6
(C) 5
(D) 7
(E) 9
Solution 1

To get the original number, we reverse the steps.

That is, we add 6 and then divide by 3 .

Therefore, the original number is $(15+6) \div 3=21 \div 3=7$.

## Solution 2

If the original number is $x$, then when it is tripled the result is $3 x$.

When this result is decreased by 6 , we get $3 x-6$.

Solving $3 x-6=15$, we get $3 x=15+6$ or $3 x=21$ and so $x=7$.

ANSWER: (D)