Simultaneous Equations Reinforcement Questions

1.

Together, Mark and Tim worked a total of 60 hours last week. Mark worked twice as many hours as Tim. How many hours did each work in the week?

First, we start by creating two equations with the information provided:

begin mathsize 14px style M a r k space plus space T i m space equals space 60 space h o u r s end style

begin mathsize 14px style M a r k space equals space 2 space cross times space T i m end style

We can then substitute the second equation into the first to solve for Tim’s hours:

begin mathsize 14px style left parenthesis 2 space cross times space T i m right parenthesis space plus space T i m space equals space 60 space h o u r s end style

Solve for Tim:

begin mathsize 14px style 2 space T i m space plus space T i m space equals space 60 space h o u r s end style

begin mathsize 14px style 3 space T i m space equals space 60 space h o u r s end style

begin mathsize 14px style T i m space equals space 20 space h o u r s end style

Knowing Tim’s hours for the week, we can then solve for Mark’s hours by substituting Tim’s hours into either equation. We will use the second equation for this example:

begin mathsize 14px style M a r k space equals space 2 space cross times space 20 space h o u r s end style

begin mathsize 14px style M a r k space equals space 40 space h o u r s end style

Of course, you could have just subtracted the 20 from 60 to get Mark’s hours but, that wouldn’t have been as much fun! 

2.

Your brewery taproom is open on a Monday night. A beer is being sold for $6.00, and a soda costs $1.00. Sales were slow that tonight, having only sold 11 items and bringing in $26.00. How many beers and sodas were sold?

As before, we start by writing out two unique equations using the information provided:

begin mathsize 14px style b e e r space plus space s o d a space equals space 11 end style

begin mathsize 14px style left parenthesis 6.00 space cross times space b e e r right parenthesis space plus space left parenthesis 1.00 space cross times space s o d a right parenthesis space equals space 26.00 end style

First, let’s get a common coefficient:

begin mathsize 14px style left parenthesis 6.00 space cross times space b e e r right parenthesis space plus space left parenthesis 6.00 space cross times space s o d a right parenthesis space equals space 66 end style

begin mathsize 14px style left parenthesis 6.00 space cross times space b e e r right parenthesis space plus space left parenthesis 1.00 space cross times space s o d a right parenthesis space equals space 26.00 end style

And now subtract one equation from another:

begin mathsize 14px style space space space bottom enclose space space space space left parenthesis 6.00 space cross times space b e e r right parenthesis space plus space left parenthesis 6.00 space cross times space s o d a right parenthesis space equals space 66
minus left parenthesis 6.00 space cross times space b e e r right parenthesis space plus space left parenthesis 1.00 space cross times space s o d a right parenthesis space equals space 26.00 end enclose
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space left parenthesis 5.00 space cross times space s o d a right parenthesis space equals space 40 end style

Rearrange to isolate soda:

begin mathsize 14px style s o d a space equals space 40 over 5 end style

begin mathsize 14px style s o d a space equals space 8 end style

OK. Now that we know we sold eight sodas that night, we now need to plug this value into either of the two original equations:

begin mathsize 14px style b e e r space equals space 11 space minus space s o d a end style

begin mathsize 14px style b e e r space equals space 11 space minus space 8 end style

begin mathsize 14px style b e e r space equals space 3 end style

We determined that last Monday, we only sold three beers. It may be time to consider some advertising or perhaps making beer people want to drink!

3.

Your company is holding a festival to celebrate 100 years in the beverage industry. Tickets went on sale, and the event was quickly sold out. A total of 1,000 tickets were available, and gross sales were $7,300. The festival is to be held on a Saturday and Sunday, and tickets are available for single days or the whole weekend. Weekend tickets cost $8.50, and one-day tickets cost $4.50. We need to know how many of each type of ticket was sold to plan the supply of drinks.

First, create two equations using the information provided:

begin mathsize 14px style left parenthesis 8.50 space cross times space w e e k e n d right parenthesis space plus space left parenthesis 4.50 space cross times space o n e space d a y right parenthesis space equals space 7 comma 300 end style

begin mathsize 14px style w e e k e n d space plus space o n e space d a y space equals space 1 comma 000 end style

Now we get to a common coefficient:

begin mathsize 14px style left parenthesis 8.50 space cross times space w e e k e n d right parenthesis space plus space left parenthesis 4.50 space cross times space o n e space d a y right parenthesis space equals space 7 comma 300 end style

begin mathsize 14px style left parenthesis 8.50 space cross times space w e e k e n d right parenthesis space plus space left parenthesis 8.50 space cross times space o n e space d a y right parenthesis space equals space 8 comma 500 end style

And now subtract one from the other:

begin mathsize 14px style space space space left parenthesis 8.50 space cross times space w e e k e n d right parenthesis space plus space left parenthesis 4.50 space cross times space o n e space d a y right parenthesis space equals space 7 comma 300
bottom enclose negative left parenthesis 8.50 space cross times space w e e k e n d right parenthesis space plus space left parenthesis 8.50 space cross times space o n e space d a y right parenthesis space equals space 8 comma 500 end enclose
space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space left parenthesis negative space 4 space cross times space o n e space d a y right parenthesis space equals space minus 1 comma 200 end style

Now we rearrange to isolate one day:

begin mathsize 14px style o n e space d a y space equals space fraction numerator negative 1 comma 200 over denominator negative 4 end fraction end style

begin mathsize 14px style o n e space d a y space equals space 300 end style

We can input this value into our simplest equation:

begin mathsize 14px style w e e k e n d space plus space 300 space equals space 1 comma 000 end style

And rearrange to isolate weekend:

begin mathsize 14px style w e e k e n d space equals space 1 comma 000 space minus space 300 end style

And calculate:

begin mathsize 14px style w e e k e n d space equals space 700 end style

4.

We have two tanks with out of specification product that needs to be blended before packaging. How many hL of 10% ABV product and how many hL of 6% ABV product must be mixed to produce 2,000 hl of 7% ABV product?

We can look at each sentence as an equation. First, we show how many hL from each tank is needed to produce 2,000 hL of 7% ABV product:

begin mathsize 14px style x space plus space y space equals space 2 comma 000 end style

We then need to think in terms of alcohol content. The first tank was at 10% ABV, and the other tank and 6% ABV. In the finished blend, we have 2,000 hL at 7% ABV or 140 hL of alcohol. This makes our two equations:

begin mathsize 14px style 0.10 x space plus space 0.06 y space equals space 140 end style

begin mathsize 14px style x space plus space y space equals space 2 comma 000 end style

We start by getting a common coefficient:

begin mathsize 14px style 0.10 x space plus space 0.06 y space equals space 140 end style

begin mathsize 14px style 0.10 x space plus space 0.10 y space equals space 200 end style

And subtracting one equation from the other:

begin mathsize 14px style space space space space 0.10 x space plus space 0.06 y space equals space 140
space bottom enclose negative 0.10 x space plus space 0.10 y space equals space 200 end enclose space
space space space space space space space space space space space space space space space minus 0.04 y space equals space minus 60 end style

Rearrange to isolate y:

begin mathsize 14px style y space equals space fraction numerator negative 60 over denominator negative 0.04 end fraction end style

And calculate the value of y:

begin mathsize 14px style y space equals space 1 comma 500 space h L end style

With this solution, we can then plug the value for y into one of the two original questions. For this example, we will use the first equation:

begin mathsize 14px style x space plus space y space equals space 2 comma 000 end style

begin mathsize 14px style x space plus space 1 comma 500 space equals space 2 comma 000 end style

Rearrange to isolate x:

begin mathsize 14px style x space equals space 2 comma 000 space minus space 1 comma 500 end style

And then calculate the value of x:

begin mathsize 14px style x space equals space 500 space h L end style

Next, we start bringing things together when we combine equations.

You have completed 0% of the lesson
0%