🔎 Plug and Chug (algebra)

If you’re stuck, you can often solve the problem using “plug and chug” (aka the Algebraic approach). With some practice, you’ll find it easy!

1. Identify the number you need and numbers you know. Need to know:

Already know:

Do you know an equation that connects the number you need to the numbers you know? 2. Plug the numbers you know into the equation. 3. Algebraically solve for the needed quantity (“chug” 🚂).

Notes:

• Math fact: If you know all of the numbers in a formula except one, you can generally use algebra to find the last number.
• This is just how you solved basic word problems in Algebra.
• Don’t forget to check your work by plugging your answer into the original equation! This is an easy way to make sure you are using this method correctly.

Problem solving template:

Using Plug and Chug: (click here for explanation)

1.) Identify equation:

Need to know -

Already know -

Equation to connect them -

2.) Plug into the equation:

3.) Solve the equation (“chug” 🚂).

⇨ Check using original equation

Example 1: Demand 1

Suppose the world daily demand for barrels of oil is given by Q^D = 155M - 1.1M*P. What price per barrel would lead to a Q^D of 42M Barrels?

Using Plug and Chug:

1.) Identify equation:

Need to know - P

Already know - Q^D = 42M

Equation to connect them - Q^D = 155M - 1.1M*P

2.) Plug into the equation: 42M = 155M - 1.1P

3.) Solve the equation (“chug” 🚂).

42M = 155M - 1.1M * P

42M - 155M = -1.1M * P (subtract 155M from both sides)

(- 113M)/(-1.1M) = P (divide both sides by -1.1)

P = $102.73

At a price of $102.73, world demand will be 42M Barrels

4.) Check using original equation

Plugging our calculated price back into the demand equation confirms that the computed demand is indeed 42M Barrels (within rounding error).

Q^D = 155M - 1.1M * P

Q^D = 155M - 1.1M * $102.73

Q^D = $42.0

Success!