# Review of past work  (Page 5/8)

 Page 5 / 8
$\begin{array}{ccc}\hfill e-F& =& -\left(F-e\right)\hfill \\ \hfill 2-11& =& -\left(11-2\right)=-9\hfill \end{array}$

You can even combine these tips: for example, you can use Tip 1 on $-10+3$ to get $3-10$ and then use Tip 3 to get $-\left(10-3\right)=-7$ .

## Negative numbers

1. Calculate:
 (a) $\left(-5\right)-\left(-3\right)$ (b) $\left(-4\right)+2$ (c) $\left(-10\right)÷\left(-2\right)$ (d) $11-\left(-9\right)$ (e) $-16-\left(6\right)$ (f) $-9÷3×2$ (g) $\left(-1\right)×24÷8×\left(-3\right)$ (h) $\left(-2\right)+\left(-7\right)$ (i) $1-12$ (j) $3-64+1$ (k) $-5-5-5$ (l) $-6+25$ (m) $-9+8-7+6-5+4-3+2-1$
2. Say whether the sign of the answer is $+$ or $-$
 (a) $-5+6$ (b) $-5+1$ (c) $-5÷-5$ (d) $-5÷5$ (e) $5÷-5$ (f) $5÷5$ (g) $-5×-5$ (h) $-5×5$ (i) $5×-5$ (j) $5×5$

## Rearranging equations

Now that we have described the basic rules of negative and positive numbers and what to do when you add, subtract, multiply and divide them, we are ready totackle some real mathematics problems!

Earlier in this chapter, we wrote a general equation for calculating how much change ( $x$ ) we can expect if we know how much an item costs ( $y$ ) and how much we have given the cashier ( $z$ ). The equation is:

$x+y=z$

So, if the price is R10 and you gave the cashier R15, then write R15 instead of $z$ and R10 instead of $y$ .

$x+10=15$

Now that we have written this equation down, how exactly do we go about finding what the change is? In mathematical terms, this is known as solving an equationfor an unknown ( $x$ in this case). We want to re-arrange the terms in the equation, so that only $x$ is on the left hand side of the $=$ sign and everything else is on the right.

The most important thing to remember is that an equation is like a set of weighing scales. In order to keep the scales balanced, whatever is done to oneside must be done to the other.

## Method: rearranging equations

You can add, subtract, multiply or divide both sides of an equation by any number you want, as long as you always do it to both sides.

So for our example we could subtract $y$ from both sides

$\begin{array}{ccc}\hfill x+y& =& z\hfill \\ \hfill x+y-y& =& z-y\hfill \\ \hfill x& =& z-y\hfill \\ \hfill x& =& 15-10\hfill \\ \hfill & =& 5\hfill \end{array}$

Now we can see that the change is the price subtracted from the amount paid to the cashier. In the example, the change should be R5. In real life wecan do this in our heads; the human brain is very smart and can do arithmetic without even knowing it.

When you subtract a number from both sides of an equation, it looks like you just moved a positive number from one side and it became a negative on the other,which is exactly what happened. Likewise, if you move a multiplied number from one side to the other, it looks like it changed to a divide. This is because youreally just divided both sides by that number and a number divided by itself is just 1

$\begin{array}{ccc}\hfill a\left(5+c\right)& =& 3a\hfill \\ \hfill a\left(5+c\right)÷a& =& 3a÷a\hfill \\ \hfill \frac{a}{a}×\left(5+c\right)& =& 3×\frac{a}{a}\hfill \\ \hfill 1×\left(5+c\right)& =& 3×1\hfill \\ \hfill 5+c& =& 3\hfill \\ \hfill c& =& 3-5=-2\hfill \end{array}$

However, you must be careful when doing this, as it is easy to make mistakes.

The following is the WRONG thing to do

$\begin{array}{ccc}\hfill 5a+c& =& 3a\hfill \\ \hfill 5+c& =& 3\hfill \end{array}$

Can you see why it is wrong? It is wrong because we did not divide the $c$ term by $a$ as well. The correct thing to do is

$\begin{array}{ccc}\hfill 5a+c& =& 3a\hfill \\ \hfill 5+c÷a& =& 3\hfill \\ \hfill c÷a& =& 3-5=-2\hfill \end{array}$

## Rearranging equations

1. If $3\left(2r-5\right)=27$ , then $2r-5=.....$
2. Find the value for $x$ if $0,5\left(x-8\right)=0,2x+11$
3. Solve $9-2n=3\left(n+2\right)$
4. Change the formula $P=A+Akt$ to $A=$
5. Solve for $x$ : $\frac{1}{ax}+\frac{1}{bx}=1$

explain and give four Example hyperbolic function
The denominator of a certain fraction is 9 more than the numerator. If 6 is added to both terms of the fraction, the value of the fraction becomes 2/3. Find the original fraction. 2. The sum of the least and greatest of 3 consecutive integers is 60. What are the valu
1. x + 6 2 -------------- = _ x + 9 + 6 3 x + 6 3 ----------- x -- (cross multiply) x + 15 2 3(x + 6) = 2(x + 15) 3x + 18 = 2x + 30 (-2x from both) x + 18 = 30 (-18 from both) x = 12 Test: 12 + 6 18 2 -------------- = --- = --- 12 + 9 + 6 27 3
Pawel
2. (x) + (x + 2) = 60 2x + 2 = 60 2x = 58 x = 29 29, 30, & 31
Pawel
ok
Ifeanyi
on number 2 question How did you got 2x +2
Ifeanyi
combine like terms. x + x + 2 is same as 2x + 2
Pawel
Mark and Don are planning to sell each of their marble collections at a garage sale. If Don has 1 more than 3 times the number of marbles Mark has, how many does each boy have to sell if the total number of marbles is 113?
Mark = x,. Don = 3x + 1 x + 3x + 1 = 113 4x = 112, x = 28 Mark = 28, Don = 85, 28 + 85 = 113
Pawel
how do I set up the problem?
what is a solution set?
Harshika
find the subring of gaussian integers?
Rofiqul
hello, I am happy to help!
Abdullahi
hi mam
Mark
find the value of 2x=32
divide by 2 on each side of the equal sign to solve for x
corri
X=16
Michael
Want to review on complex number 1.What are complex number 2.How to solve complex number problems.
Beyan
yes i wantt to review
Mark
use the y -intercept and slope to sketch the graph of the equation y=6x
how do we prove the quadratic formular
Darius
hello, if you have a question about Algebra 2. I may be able to help. I am an Algebra 2 Teacher
thank you help me with how to prove the quadratic equation
Seidu
may God blessed u for that. Please I want u to help me in sets.
Opoku
what is math number
4
Trista
x-2y+3z=-3 2x-y+z=7 -x+3y-z=6
can you teacch how to solve that🙏
Mark
Solve for the first variable in one of the equations, then substitute the result into the other equation. Point For: (6111,4111,−411)(6111,4111,-411) Equation Form: x=6111,y=4111,z=−411x=6111,y=4111,z=-411
Brenna
(61/11,41/11,−4/11)
Brenna
x=61/11 y=41/11 z=−4/11 x=61/11 y=41/11 z=-4/11
Brenna
Need help solving this problem (2/7)^-2
x+2y-z=7
Sidiki
what is the coefficient of -4×
-1
Shedrak
the operation * is x * y =x + y/ 1+(x × y) show if the operation is commutative if x × y is not equal to -1
A soccer field is a rectangle 130 meters wide and 110 meters long. The coach asks players to run from one corner to the other corner diagonally across. What is that distance, to the nearest tenths place.
Jeannette has $5 and$10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
What is the expressiin for seven less than four times the number of nickels
How do i figure this problem out.
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why surface tension is zero at critical temperature
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I think if critical temperature denote high temperature then a liquid stats boils that time the water stats to evaporate so some moles of h2o to up and due to high temp the bonding break they have low density so it can be a reason
s.
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
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