Different Options for Solving One Equation

Student Summary

Equations can be solved in many ways. In this lesson, we focused on equations with a specific structure, and two specific ways to solve them. 

Suppose we are trying to solve the equation 45(x+27)=16\frac45(x+27)=16. Two useful approaches are:

  • Divide each side by 45\frac45.
  • Apply the distributive property.

In order to decide which approach is better, we can look at the numbers and think about which would be easier to compute. We notice that 4527\frac45 \boldcdot 27 will be hard, because 27 isn't divisible by 5.  So, distributing the 45\frac45 is not the best method. But 16÷ 4516 \div \frac45 gives us 165416 \boldcdot \frac54, and 16 is divisible by 4. So, dividing each side by 45\frac45 is a good choice.

45(x+27)=165445(x+27)=1654x+27=20x=-7\begin{aligned} \tfrac45 (x+27) &= 16 \\ \tfrac54 \boldcdot \tfrac45 (x+27) &= 16 \boldcdot \tfrac54 \\ x+27 &= 20 \\ x &= \text- 7 \\ \end{aligned}

Sometimes the calculations are simpler if we first use the distributive property. Let's look at the equation 100(x+0.06)=21100(x+0.06)=21. If we first divide each side by 100, we get 21100\frac{21}{100}  or 0.21 on the right side of the equation. But if we use the distributive property first, we get an equation that only contains whole numbers. 

100(x+0.06)=21100x+6=21100x=15x=15100\begin{aligned} 100(x+0.06) &= 21 \\ 100x+6 &= 21 \\ 100x &= 15 \\ x &= \tfrac{15}{100} \\ \end{aligned}

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