2.1.4 Practice: Adding Rational Numbers
1 answer:
You might be interested in
Part (a)
- x = number of bass caught
- y = number of trout caught
x and y are nonnegative whole numbers.
3x represents the total weight of all the bass, since one bass weighs 3 pounds. Similarly, 2y is the total weight of the trout with each one being 2 pounds. Adding up all the weight of all the fish, we get 3x+2y. This is set equal to 34 pounds which is the total stated weight caught.
In short, we end up with the equation 3x+2y = 34
Now onto the second equation. The expression 5x represents how many points Pat gets from catching x bass, because he gets 5 points per bass. Then we subtract off 2y to represent Pat losing 2 points per trout he catches. Overall, his point total is 5x-2y. This is set equal to his point total of 14.
The second equation is 5x-2y = 14
------------
Answer:
3x+2y = 34
5x-2y = 14
Both equations are needed to form this particular system.
===================================================
Part (b)
We could use a number of methods to solve for (x,y). Possibly the most efficient is elimination. Why? Because note how we have 2y up top and -2y down below. They add to 0y which is just 0. The y terms go away, and are eliminated. Afterward, all we're left with is x in which we can solve for just like any other single variable equation. More info is in part (c).
===================================================
Part (c)
Refer to the answer in part (a). We'll add straight down. So that means we have these three sets of addition operations.
- 3x+5x becomes 8x
- 2y + (-2y), aka 2y-2y, becomes 0y and the y terms go away
- 34+14 simplifies to 48
After those three sets of addition operations, we're left with the much simpler equation 8x = 48. To solve this, we divide both sides by 8 and we get x = 6. This says Pat caught 6 bass.
Use this value of x to find y. So we'll plug x = 6 into either equation involving x,y and solve for y
3x+2y = 34
3(6)+2y = 34
18+2y = 34
2y = 34-18
2y = 16
y = 16/2
y = 8
So we can see that Pat caught 8 trout as well.
The check portion is shown in the attached image below. Effectively, all we're doing is replacing x and y with 6 and 8 respectively. Then we're simplifying both sides. Getting the same number on both sides results in a true equation, and therefore verifies we have the correct (x,y) solution.
Solution: (x,y) = (6,8)
Interpretation: Pat caught 6 bass and 8 trout
