mustangman8037
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In 5 years, Leroy will be twice as old as his brother. Today, their ages add up to 14.
How old is Leroy?
How old is his brother?
How old is Leroy?
How old is his brother?
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Parent in need of help with 4th grade algebra
- Thread starter mustangman8037
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mustangman8037 said:In 5 years, Leroy will be twice as old as his brother. Today, their ages add up to 14.
How old is Leroy?
How old is his brother?
Since I'm not familiar with algebra taught at the fourth grade level, I wonder if you might be able to show us what your fourth-grader has tried.
I'd suggest that maybe an appropriate approach for a fourth-grader might be the "guess and check" method.
We know that Leroy and his brother's ages add up to 14 today. And it looks like Leroy is the oldest, since in 5 years, he'll be twice as old as his brother.
Take a guess...maybe Leroy is 8 and his brother is 6 now. Their ages would add up to 14.
In 5 years, how old would Leroy be? Well, 8 + 5 is 13, so in 5 years, Leroy would be 13. And how old would his brother be in 5 years? If the brother is now 6, in 5 years, the brother would be 6 + 5, or 11 years old. Would Leroy's age be twice his brother's age then? No...13 is NOT twice as old as 11. So, our guess of 8 and 6 as their present ages is not correct. And, since we need their ages in 5 years to be further apart than 13 and 11, we need to modify our guess about their present ages to make their present ages further apart.
Might want to try 11 and 3 for their present ages....check to see if that guess gets you closer.
Hello, mustangman8037!
Systems of equations . . . in fourth grade?
Let \(\displaystyle L\) = Leroy's age now.
Let \(\displaystyle B\) = brother's age now.
In five years, they will both be 5 years older.
. . Leroy will be \(\displaystyle L + 5\) years old.
. . His brother will be \(\displaystyle B + 5\) years old.
"Leroy will be twice as old as his brother":
. . \(\displaystyle L + 5 \:=\:2(B+5) \quad\Rightarrow\quad L - 2B \:=\:5\) .*
"Today their ages add up to 14":
. . \(\displaystyle L + B \:=\:14\) .*
\(\displaystyle \text{We have a system of equations: }\;\begin{array}{ccccc} L - 2B &=& 5 & [1] \\ L + B &=& 14 & [2] \end{array}\)
\(\displaystyle \text{Subtract [2] - [1]: }\;3B \:=\:9 \quad\Rightarrow\quad B \:=\:3\)
\(\displaystyle \text{Substitute into [2]: }\:L + 3 \:=\:14 \quad\Rightarrow\quad L \:=\:11\)
Leroy is 11; his brother is 3.
Systems of equations . . . in fourth grade?
In 5 years, Leroy will be twice as old as his brother.
Today, their ages add up to 14.
(a) How old is Leroy?
(b) How old is his brother?
Let \(\displaystyle L\) = Leroy's age now.
Let \(\displaystyle B\) = brother's age now.
In five years, they will both be 5 years older.
. . Leroy will be \(\displaystyle L + 5\) years old.
. . His brother will be \(\displaystyle B + 5\) years old.
"Leroy will be twice as old as his brother":
. . \(\displaystyle L + 5 \:=\:2(B+5) \quad\Rightarrow\quad L - 2B \:=\:5\) .*
"Today their ages add up to 14":
. . \(\displaystyle L + B \:=\:14\) .*
\(\displaystyle \text{We have a system of equations: }\;\begin{array}{ccccc} L - 2B &=& 5 & [1] \\ L + B &=& 14 & [2] \end{array}\)
\(\displaystyle \text{Subtract [2] - [1]: }\;3B \:=\:9 \quad\Rightarrow\quad B \:=\:3\)
\(\displaystyle \text{Substitute into [2]: }\:L + 3 \:=\:14 \quad\Rightarrow\quad L \:=\:11\)
Leroy is 11; his brother is 3.