Question

solve by elimination
0.3x-0.2y=4
0.4x+0.3y=-1

Answer 1

muliply by 10 to get rid of the decimals... that will make it look less intimidating

Answer 2

3x-2y = 40
4x +3y = -10

Answer 3

if you multiply 40 on the first eqn
and 30 on the second, you can see which ones can be eliminated

Answer 4

your idea is to make the coefficients of either x or y to be equal

Answer 5

for most elimination problems, that will work

Answer 6

to eliminate the x variables; *4 the top and *3 the bottom...then subtract

Answer 7

12x -8y = 160
12x +9y = -30

Answer 8

we could combine these steps by mulitply one equation by a negative instead...

12x -8y = 160
-12x -9y = 30
---------------
-17y = 190

y = -190/17

Answer 9

you lost me

Answer 10

where?

Answer 11

12x-8y=160
12x-9y=-30
how did you get those

Answer 12

by subtraction......
12x -8y = 160 12x -8y = 160
-(12x +9y = -30) means -12x -9y = 30
---------------- ----------------

Answer 13

tell me: does this equal out?

5 5
-(-4) +4
---- ---- ???

Answer 14

yes

Answer 15

thats all i did..... just with more numbers involved

Answer 16

how did you get the 12x -8y = 160 & -(12x +9y = -30)

Answer 17

elimination means 'get rid of something'...right?


the only way to get rid of something; to eliminate it; is to get it to zero... otherwise there is something still there right?

Answer 18

right

Answer 19

you are given 2 equations and are asked to eliminate something.... that would either be the xs or the ys right? I choose the xs cause they were in front.

Answer 20

ok

Answer 21

do you recall that in an equation..whatever you do to one side has to be done to the other to keep it equal?

Answer 22

yes

Answer 23

5+3 = 8 when we multiply this by 4 is it still equal?

4(5+3 = 8)..... 20 + 12 = 32 ???

Answer 24

right

Answer 25

do the variables make a difference to it?

4(5x + 3y = 4)......20x +12y = 16...still equal??

Answer 26

we are not changing the 'value'...just the form, its shape, the way it looks..... the value remains the same. right?

Answer 27

right

Answer 28

so lets use this to our advantage..

we want some part of your equation to cancel each other out...

what wer ethe equations again?

Answer 29

0.3x-0.2y=4
0.4x+0.3y=-1

we can multiply both equation by 10 to get rid of the decimal and make it easier to look at right? we change the shape; but not the value

Answer 30

k

Answer 31

3x - 2y = 40
4x +3y = -10 we good here?

Answer 32

yes

Answer 33

we have no terms that are the same...so we have to modify some more..... to get rid of one of them.....or rather a set of them.

Answer 34

if we pick 'x'...what value do 4x and 3x have in common?

Answer 35

x?

Answer 36

x is not a 'value' :) 4x and 3x..... do they have 12x in common? 8x? 29x?

Answer 37

x is a valued pick; but that makes things messier lol

Answer 38

valid pick is what its spose to say...

Answer 39

4x(3) = 12x

3x(4) = 12x.....right?

Answer 40

right

Answer 41

so the top can be *4; and the bottom *3

4(3x - 2y = 40) 12x -8x =160
3(4x +3y = -10) 12x +9y = -30


havent changed anything but the way they look correct?

Answer 42

correct

Answer 43

but if we add these together...nothing is eliminated is it?... what do we have to do to get an elimination now?

Answer 44

wouldnt x be eliminated

Answer 45

how? 12x + 12x = 24x..... that aint zero..

Answer 46

your right i was thinking bout -12x +12x
continue plz

Answer 47

thats right... we need to change the way one of them looks again to get a -12x...

12x -8x =160 12x -8x =160
-1(12x +9y = -30) -12x -9y = 30..now were good to go

Answer 48

can we eliminate now?

Answer 49

yes

Answer 50

we get:

-17y = 190..... solve for y

y = -190/17. right?

Answer 51

yes

Answer 52

since we have a solid value for y...use it to find x

Answer 53

wait how does 190 become -190 and -17 becomes 17

Answer 54

the negative doesnt care what its attached to..... any (+)(-) combonation results in a (-)...right?

does 190/-17 equal something different than -190/17?

Answer 55

i guess not

Answer 56

the proper ettiquiette is to put the sign to the top...

Answer 57

but in some cases its good to know that you can move it around

Answer 58

what wouldve hapened aif we combined steps?

Answer 59

.4(.3x -.2y = 4) .12x -.08y = 1.6
-.3(.4x+.3y =-1) -.12x -.09y = .3
-----------------
-.17y = 1.9


y = -1.9/.17 = -190/17

Answer 60

right

Answer 61

0.4x+0.3y=-1

.4x + .3(-190/17) = -1....solve for x

Answer 62

-5.7

Answer 63

or is it -133/17

Answer 64

4x = -10 + 570/17

4x = (-170 + 570)/17

4x = 400/17

x = 400/4.17 = 100/17

Answer 65

4.17 is a lazy way of writing 4*17

Answer 66

how did yiu get 570/17

Answer 67

i used 3(-190/17) instead of .3(-190/17)

3(-190) = -570
------ ------
17 17


4x - 570/17 = -10

4x = -10 + (570/17)...

Answer 68

oh ok i was doing it by .3

Answer 69

:) .3 was fine, but you would have had to change the decimal eventually

Answer 70

1/.17 cahnges to 100/17

Answer 71

-10*17=-170

Answer 72

.4x + .3(-190/17) = -1

.4x - 57/17 = -1

.4x = -1 + (57/17)

.4x = (-17+57)/17

.4x = 40/17

x = 40/(.4*17)

x = 400/(4*17)

x = 100/17

Answer 73

ok i think i got it

Answer 74

i think i see you trying to get rid of the 17 on the bottom :)

Answer 75

i just dont know how to do this stuff

Answer 76

taking midterms this week these questions are for the practice exam

Answer 77

68x - 570 = -170

68x = -170 + 570

x = 400/68

x = 400/4 100
------- = -----
68/4 17

Answer 78

i got a final grade of 89.06%...and it gave me an 'A' for the course ;)

Answer 79

i dropped 3 writing assignments and still passed with an 'a' lol

Answer 80

thats good!
right now i have a 77.37%

Answer 81

how did you get those answers above 68x....

Answer 82

i times everything by 17 to get rid of the fraction...

Answer 83

4(17) = 68

Answer 84

right but 3(17)=51

Answer 85

3(-190)(17)
---------- = 3(-190)
(17)

Answer 86

17/17 = 1

Answer 87

x=400/68 i divide that by?

Answer 88

thats why its called getting rid of a fraction ;)

Answer 89

400/68 has 4 in common..remember 4(17)? and 4(100) = 400

Answer 90

divide them both by 4

Answer 91

ok now that way makes sense to me

Answer 92

you seem to see numbers and math is a solid concrete building that cant be moved or messes with.

but its really more like silly putty...bend it to your will :)

Answer 93

algebra has 5 rules: and only 5 rules...

Answer 94

whats that?

Answer 95

1. numbers can be moved around (commutative)
2. numbers canbe grouped in different ways (associative)
3. every number has an evil twin (inverse).
4. there is one number that changes nothing (identity)
5. distribute numbers thru paranthesis (distributive)

Answer 96

i will have to make a note of those

Answer 97

3 and 4 are split in 2 by some people to get an additivie inverse/multiplicative inverse and an additive indentity/multiplicative identity

Answer 98

tell me; the 1st rule says we can move number around...

4-5 is the same as -5+4 right?