[scheduled:: 2025-01-15]

Multivariable Word Problems

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Vera and Vikki are sisters. Vera is 4 years old and Vikki is 13 years old. What age will each sister be when Vikki is twice as old as Vera?

What's the data?

What's the unknown?

How do you pick the unkown?

This one is tricky - it's not any of the named parts! Start by making an expression for each sister's age after some amount of time:
let a = Vikki's age
let b = Vera's age
Vera's age after $n$ years is $4 + n$
Vikki's age after $n$ years is $13 + n$
Notice we have another variable: $n$ , which is the number of years

We're looking for the time when $a = 2 b$ , but $a$ and $b$ depend on n...
What about solving for $n$ ?

$2 (4 + n) = 13 + n$
$2 n + 8 = n + 13$
$n = 5$

So, Vikki will be twice Vera's age in 5 years, or when she is 18 and Vera is 9.

For this problem, they never actually asked for the right unknown. We had to figure out what it was by exploring the problem.

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Do problems from IXL word problems as guided practice together on the whiteboard