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Evaluating expressions with two variables
Description
Exercise Name: Evaluating expressions with two variables
Math Missions: 6th grade (U.S.) Math Mission, Algebra basics Math Mission, Algebra I Math Mission, Mathematics II Math Mission
Types of Problems: 1

The Evaluating expressions with two variables exercise is located in the 6th grade (U.S.) Math Mission, Algebra basics Math Mission, Algebra I Math Mission and Mathematics II Math Mission.

## Types of problems

1. Evaluate the following expression when ${x}$ equals a number; ${y}$ = a number: This problem gives users an expression with two unknowns along with a number. The user is required to substitute the value of those two unknowns into the expression and evaluate it.

## Strategies

It is hard to get the accuracy badges and speed badges in this skill. Substituting the numbers to the unknowns and evaluating the entire expression may take 15-20 seconds.

## Real-life Applications

1. Knowledge of algebra is essential for higher math levels like trigonometry and calculus. Algebra also has countless applications in the real world.
2. Work problems often ask us to calculate how long it will take different people working at different speeds to finish a task. The algebraic models of such situations often involve rational equations derived from the work formula, ${W = rt}$. The amount of work done (${W}$) is the product of the rate of work (${r}$) and the time spent working (${t}$). The work formula has 3 versions:
${W = rt}$
${t = \frac{W}{r}}$
${r = \frac{W}{t}}$