"Thinking backwards"-starting at the end of the problem and using reverse operations-can help you solve certain problems at different grade levels.
a)
Write an equation that describes this problem.
b) What is the original number?
Answer:
a) We're looking for a certain (unidentified) number,
x. "x, quadrupled" means "
4x." Then, we add 3 to the answer, so 4
x + 3. We then
triplethe quantity "4
x + 3
":
3(4
x + 3). Finally, we split the quantity 3(4
x + 3) in
half in order to yield the final answer, 12, so {3(4
x+ 3)}
/2 = 12.
b)
To find the original number, we solve for
x, which involves "canceling out" the numbers by using inverse operations.
So,
(2){3 (4
x + 3)}
/2 = 12
(2) multiply both sides by 2...
{
3(4x + 3)}
/3 = 24
/3divide both sides by 3...
4x
+ 3- 3 = 8
- 3 subtract 3 from both sides, and...
4x
/4= 5
/4 divide both sides by 4.