Test corrections(Solving equations,Ops w/ #'s and variables)

[Mizuki]

Is there anyone that can walk me through most of these test corrections? I'm afraid I'm going to fail if I don't get some help from someone, and at this time of day you guys are the only help I can get, my parents refuse to help me because they say "They forgot it after college" D:

The Problems:

1f.) a^2b - 3ab^2 - 2a^3b^3 = I got 114
if a = -2 and b=3
2a.) 3x + 7 = 13

I got x = 6

2b.) 3(2x - 4) = 10 - 4(3 - x)

I got 3.3 = -6x

3a.) Five times a number is decreased by eight, the result is then -43. What is the number?

I got 5n - 8 = -43
n = app. 10.2

3b.) A number is increased by eleven and the sum is then tripled. The result equals 78. Find the number.

I got (n + 11)3 = 78
n= 15

I got these all wrong on the test, and I can't find out how to do them right! I really really want to get rid of the nasty F that is my test, so I want someone to walk me through these, and maybe next time I wont get such a bad grade. Please help!

 

[mts]

If it is this,

(a^2)(b) - (3)(a)(b^2) - (2)(a^3)(b^3)

if a = -2 and b=3

then:

= (-2^2)(3) - (3)(-2)(3^2) - (2)(-2^3)(3^3)

= (4)(3) - (3)(-2)(9) - (2)(-8)(27)

= 12 - (-54) - (-432)

= 12 + 54 + 432

= 498

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

3x + 7 = 13

Subtract 7 from both sides

3x = 6


x = 2

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

3(2x - 4) = 10 - 4(3 - x)

Expand, remember (-4) *(-x) = 4x

6x - 12 = 10 -12 + 4x

Subtract 4x from both sides

2x - 12 = 10 - 12

Add 12 to both sides

2x = 10

x = 5

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Five times a number is decreased by eight, the result is then -43. What is the number?

5n - 8 = -43

add 8 to both sides

5n = -35

n = -7

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A number is increased by eleven and the sum is then tripled. The result equals 78. Find the number.

(n + 11)3 = 78

Divide both sides by 3

n + 11 = 26

Subtract 11 from both sides

n = 15

Work through these solutions, please check the answers by making sure they work in the original equations. If any steps are not clear please ask.