math help!!!! please?

Question

does this look right i'm doin combining like terms

1. 7(2 - 4y) + 14y =42
14 - 28y + 14y = 42
1 - y = 3
y = -2

2. 5b - 3/4 b + 6 = 1/4
20b -3b + 24 = 1
17b = -23
b = -23/17

3. 3x + 6 = 12x + 24
-18 = 9x
x = -2

4. 0.4c = 0.7c - 2.7
4c = 7c -27
27 = 3c
c = 9


ok so do u think this looks rite...i wanna make sure i'm doin it rite so thanx 4 ur help!!!=))

Answer 1

1.) 7(2 - 4y) + 14y = 42
7(2) - 7(4y) + 14y = 42
14 - 28y + 14y = 42
14 - 14y = 42
-14y = 28
y = -2

2.) 5b - 3/4b + 6 = 1/4
4 1/4b + 6 = 1/4
4 1/4b = - 5 3/4
b = -10

3.) 3x + 6 = 12x + 24
6 = 9x + 24
-18 = 9x
-2 = x

4.) 0.4c = 0.7c - 2.7
- 0.3c = -2.7
c = 9

I just felt like doing them myself :), but you got all right except 2

Answer 2

try this. When you are combining like terms, you need to do just that. It's been a while, but here goes:

7(2-4y)+14y=42
step one: remove the parentheses
7(2) =14 7(-4y) =-28y
step two: put them back into the equation
14-28y+14y=42
step three: combine like terms
-28y+14y=-14y
step four: put 'em back
14-14y=42
simplify: combining like terms again, I guess
(-14+14)-14y=(42-14)
0-14y=28
-14y=28
now divide -14 from both sides
y=-28/14
simplify
y=-2

Answer 3

The quickest way to check is to put your answer into the equation and calulate it out:
so, for #1, 7(2-(4*-2)) + (14*-2) = 42
becomes 7(2+8) + -28 = 42
becomes 70 - 28 = 42. looks good to me!

For #2, (5*-23/17) - (3/4*-23/17) + 6 = 1/4
becomes -115/17 - (-69/68) + 6 = 1/4
becomes -460/68 + 69/68 + 408/68 = 1/4.
becomes 477/68 - 460/68 = 1/4
becomes 17/68 = 1/4. looks good to me!

For #3, (3*-2) + 6 = (12*-2) + 24
becomes -6 + 6 = -24 + 24. looks good to me!

For #4, (0.4*9) = (0.7*9) - 2.7
becomes 3.6 = 6.3 - 2.7 looks good to me!

Excellent job!