Pre-Algebra help, please?

Question

Simplify.

8. 6b+5-6b
9. 7x+2-8x+5

Solve.

11= 1/3a+2
12. -2k+7=-3

18. Write and solve an equation to find the value of x so that the polygons have the same perimeter. Polygon 1: 2x, x+2, x+2, 4x+1. Polygon 2: 6x, 2x, 2x+2


20.The length of a rectangular room is 3 feet more than twice its width. If the perimeter of the room is 78 feet, find its width.


I've already tried solving these on my own, but I keep getting them wrong. Any help would be appreciated.

Answer 1

For the first 2, you just need to combine like terms, 6b-6b cancels out, leaving you the +5 for your simplification, and 7x-8x is -x, and 2+5 is 7, leaving -x+7 for your simplification.



I'm not sure about 11, unless there is a typo, but for 12, you need to isolate the variable, subtract 7 from both sides, leaving you -2k = -10, then divide both sides by -2, making k=5.



For 18, I would draw 2 polygons, label the sides (it doesn't matter how you make your shapes, as long as each side is represented). I do this for a visual picture of the question. Since you add all sides to get the perimeter, and you want the perimeters to be the same, set each polygon equal to eachother:

2x + (x+2) + (x+2) + (4x+1) = 6x + 2x + (2x+2) Since all of your signs are +, you can drop your parenthesis and combine like terms:

2x+x+2+x+2+4x+1 = 6x+2x+2x+2:

8x+5 = 10x+2 Now solve:

-8x -8x

____________

5 = 2x+2

-2 -2

___________

3 = 2x

Then divide both sides by 2, giving you x = 3/2



OK, for 20, draw another picture and label your sides. So, if the length, or L, is 3 feet more than (plus) twice (multiply by 2) the width, or w, then your long sides should be labeled as 2w+3, and your short sides are just w. If the perimeter is all the sides added together, we can make the equation look like this:

(2w+3) + (2w+3) + w + w = 78 OR

2(2w+3) + 2w = 78 Then just solve it:

Distribute the 2 into the 2w+3:

4w+6+2w = 78 Combine like terms:

6w+6 = 78 Subtract 6 from both sides:

-6 -6

_________

6w = 72

Divide both sides by 6:

w = 12

Answer 2

Jenna,



BIG TIP: Post one question at a time or else your questions will be ignored.



20.The length of a rectangular room is 3 feet more than twice its width. If the perimeter of the room is 78 feet, find its width.





length = 2x + 3



width = x



perimeter = 78



Use P = 2l + 2w



78 = 2(2x + 3) + 2(x)



78 = 4x + 6 + 2x



78 = 6x + 6



78 - 6 = 6x



72 = 6x



72/6 = x



12 = x



The width is 12 feet.

Answer 3

For these all you do is combine the terms that have the same variable and stuff

8. 5

9. -x+7



11. you subtract 2 from both sides so you get 9=1/3a then you multiply both sides by the reciprocal (3/1) and a=27

12. subtract 7 from both sides, -2k=-10 then divide by -2 and so k=5



thats all i got