Tom is 5 years younger than Lisa. In 6 years, Tom will be 3/4 as old as Lisa. How old is Tom now?
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- เผยแพร่เมื่อ 28 เม.ย. 2024
- How to solve an algebra age word problem - linear equations. Learn more math at TCMathAcademy.com/.
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It's good that you give an example of these types of problems with fractions in them. Students need more exposure to fractions in order to reduce their aversion to them -- which many may still have, even when they get to algebra.
I missed multiplying through by 4, and solved this with the fractions to the very end. (I used L for Lisa's age). So at the end I had 1/4L = 14/4. Then multiplied by 4: L = 14. Subtract 5 for Tom.
Do you find that many of your students benefit from using a table? Hopefully, by the time they get to the SAT, they won't need that any more. It is time-consuming.
It would have been much easier to follow if you had used L for Lisa's age and T for Tom's age. There is no law that says you have to use X and Y.
Thank you.
Original question omitted as lisa when referring to 3/4 as old.
got it 9 thanks for the fun.
As the age required was Tom’s I wonder why the solution starts with the age of Lisa as the unknown « x »? It introduces an extra risk of mistakes.
It's the risk that makes math so exciting. 😀
Because we only know Tom's age + 6 as a proportion of Lisa's age + 6. So we can't find The former without first finding the latter. (If you check out my comment, I broke it down into stages instead of putting it all into a single equation. The result is the same, but it might make the logic a little clearer.)
Got it, it is 15 to 20.
Tom is 9 years old
9
Let Lisa's age in 6 years be x
Let Tom's age in 6 years be y
Let Tom's age now be z
x − 5 = 0.75x
x = 0.75x + 5
x − 0.75x = 5
0.25x = 5
x = 20
y = 20 × 0.75
y = 15
z = 15 − 6
z = 9
How is 9 3/4 of 14?
No 3/4 of 20 is the age of Lisa in 6 years. So Tom will be 15 in 6 years and subsequently is 9 now.
It isn't. But in 6 years they'll be 15 and 20, and that's when the question says Tom will be 3/4 Lisa's age.
Tom is 9 years old