# math

2x + 3y = 78
How do i solve for x and y?

2x=78
78/2=39 so x=39

3y=78
78/3=26 so y=26

Can't be, because 2(39)+ 3(26) does not equl 78

You need TWO equations when you have TWO variables, such as x and y. It can't be done with one equation. BUT, you say, what about this post giving x as 39 and y as 26.
To determine if the first answer posted is correct, simply put the numbers back into the equation and see if the equation is satisfied.
2x + 3y = 78
2*39 + 3*26 = 78
78 + 78 = 78?? OOPS!.
So x = 39 and y = 26 isn't correct. Ya gotta have two equations. I hope this helps.

2x + 3y = 78
3x + 2y = 72

Here is the original question: Pencils have one price and pens have another. Two pencils and three pens cost 78 cents, but three pencils and two pens cost 72 cents. How much does one pencil cost?

Use variable x for pencils and y for pens.

2x + 3y = 78
3x + 2y = 72

In the first equation, solve for y.

2x + 3y = 78
3y = 78 - 2x
y = (78 - 2x) / 3

Substitute this value for y into the second equation.

Hers is another one: 3 people requires 3 weeks and 2 days to do a job. How long would it take for 4 people to do the same job? (Each week is 6 days)

48

1--2x + 3y = 78
2--Divide through by 2 yielding x + y + y/2 = 39
3--y/2 must be an integer k making y = 2k
4--Substituting, 2x + 6k = 78 making x = 39 - 3k.
5--k....0....1....2....3....4....5....6
...x...39...36...33...30...27...24...21
...y...0....2.....4...6....8....10...12

...k...7...8...9...10...11...12...13
...x..18..15..12...9....6....3....0
...y...14.16..18...20...22...24...26

65

1. 👍 0
2. 👎 0
3. 👁 486
1. -9x-13-9x=-31

1. 👍 0
2. 👎 0
posted by gurleen

## Similar Questions

1. ### Math

We have an important chemsitry test due and I want to make sure that I do not mess up on my algebra. I am dealing with the integrated rate law, but my question is purely algebraically in nature. I hope, somebody can help me. 1)

asked by Yasemine on May 13, 2013
2. ### math

actually, in a addition to the question i posted a few minutes ago, can someone please help me with a few actual specific questions? thanks so much i'm very confused and i've been working on these all day. *Literal Equations*

asked by kim on October 26, 2007
3. ### algebra

Solve the indicated variable: 1. Volume of a cone: solve for h: V=¨ir^2h/3 2. Temperature formula: solve for C: F=9/5C+32 pleaseeeee help me solve these! plzzz! i have nooo idea how to do these. THANKS! =)))

asked by kitty kat on September 20, 2009
4. ### Alebra

Solve 5m - 8 > 12 Solve 12 - 3a > 18 Solve 5m - 4 < 2m + 11 Solve 2r - 18 ≤ 5r + 3 Solve 26p - 20 > 14p + 64 Can someone give me an example to one of these? I don't know how to do these.

asked by Jessi on December 19, 2016
5. ### Substitution Method-Plz help

Use the Substitution method to solve the system of equations. x + y = -4 x - y = 2 solve for x in the second equation. x= y+2 Put that in for x in the first equation: x+y=-4 (y+2) + y = -4 solve for y. Then, x= y+2 i don't get

asked by Svetlana on October 17, 2006
6. ### Intermediate Algebra

Combine like terms: -3x^2+2x-4x^2-9+6x-2x^2+8 Solve for x: 8x-11= -11x+18 Solve for x: -2(x-5)+7=z-8-5x Solve for x: (x-2)/5 - 3/2= (x+1)/10 Translate to an algebra statement; do not solve: Seven times the difference of six and a

asked by Dawn on September 29, 2007
7. ### Algebra

To solve the system of equations, which expression could be substituted for x into the first equation? 3x-5y=14 x+4y=10 a)10-4y b)4y+10 c)(1/4)x+(5/2) d)(-1/4)x+(5/2) I have another problem just like this one so if you could

8. ### Math

I just don't understand this question: h(t)=A*b^x h(3)=4 h(5)=40 Solve for b Would you plug 3 into the x and set it equal to 4? (4=A*b^3) How would you solve for that because in the next question they go on to ask you to solve for

asked by Nicole on August 30, 2006
9. ### Math

Solve by eliminnation methods 2x-4y=5 2x-4y=6 solve the system by elimination method 5x+2y= -13 7x-3y=17 Solve x+64 Determine whether the given numbers are solutions of the inequality 8,-10,-18,-3 y-8>2y-3 Solve by the

asked by jay jay on July 14, 2008