Vanity... 4 [4 - 5x] = 6x + 4

high school ^ | n/a | n/a

[The SISU kid]

I know there a a lot of FReepers smarter than I, so here goes...got this presented to me for help & I for the life of me am stumped

4 [4 - 5x] = 6x + 4

says answer is x= 10/7

can someone show how to solve?

Thanks in advance....

[BradyLS]

I hate calculators, because they weaken our skills. They are great for speeding up things, but horrible for increasing our math skills.

If it were up to me, calculators would be banned until college, to which you’d then take a first semester course on how to use one.

I think you should have to know how to do everything with a pencil, sheet of paper, and the appropriate charts.

Bump and repeat!

Parent should tell their kids to learn the first universal language: mathematics. Learn your native language. Learn to write well in it. Then ace math in high school and onward; learn the hard sciences; and study some form of engineering and you can do anything you want in life.

[ApplegateRanch]

Not now, it doesn’t; says 6/13

---

4 (4-5 x) = 6 x+4
Mathematica plaintext input:
4 (4 - 5 x) == 6 x + 4

Mathematica plaintext output:
{{x == 6/13}}

[Peter ODonnell]

I asked a climate scientist, he says

x = polar ice caps will melt in 2018

[SamAdams76]

Growing up in school, I never did see why I should be expected to solve for "x". My opinion was that "x" ought to be a little more self-sufficient so that it could solve for itself. I've got my own problems.

I think that might have been the beginning of my conversion to conservatism.

[Peter W. Kessler]

The title of this post, for me, is “Why I Majored in History.”

[Maurice Tift]

Sometimes your answer doesn't match the answer in the back of the book.

Backs of books are written by people and people are no good.

[KSCITYBOY]

btt

[TheSarce]

Aw heck, I thought this might rival THIS thread from last year, which went over 650 replies:

48÷2(9+3) = ?

(I was going to say "my HS Algebra teacher must be rolling in his grave over all this confusion," but to my astonishment, a quick google search indicates he's still alive!)

[fteuph]

The brackets around “4-5X” mean that this is the absolute value of the terms, i.e. always has a positive value.

Parenthesis around the terms would denote just a simple multiplication.

My algebra is a bit fuzzy these days, but I believe both answers would be correct.

Nice work, SISU kid!

[Leroy S. Mort]

They told me there would be no math here.

[aruanan]

48÷2(9+3) = ?

2? Because one starts inside the parentheses and works outward?

[FourPeas]

If I’d only thought of that 35 years ago....

[MHGinTN]

It does appear the problem was miss copied, to get a different answer to drop out; the first ‘4’ should read ‘-4’, to get the answer dictated.

[Ingtar]

I copy/pasted the assumed answer from the original post and forgot it was down there...

[cynwoody]

UPDATE: 10/7 is the answer....thru a text message misinturppration...

4 abs(4 - 5x) = 6x + 4

I assumed the absolute values marks were brackets....my bad

Wolfram finds two solutions to the absolute-value version: 6/13 and 10/7.

[raygun]

4 * |4 -5x| = 6x + 4 results in two solutions:

|4 - 5x| = (6/4)x + 4/4

4 - 5x = -(6/4)x - 1 or (6/4)x +1

4 = -(6/4)x + 5x -1 or (6/4)x +5x +1

5 = -(6/4)x +5x or 3 = (6/4)x + 5x

5 = -(6/4)x + (20/4)x or 3 = (6/4)x + (20/4)x

5 = (14/4)x or 3 = (26/4)x

20 = 14x or 12 = 26/x

20/14 = x or 12/26 = x

10/7 = x or 6/13 = x

[Cyber Liberty]

Because one starts inside the parentheses and works outward?

Correctamundo. You picked a good example because it's my understanding a TI calculator will give you the incorrect answer because it (at least the earlier models) implements the parentheses incorrectly. I admit to the possibility it's my memory that is in error.

[aruanan]

it's my understanding a TI calculator will give you the incorrect answer because it (at least the earlier models) implements the parentheses incorrectly.

That sounds familiar.

[Cyber Liberty]

That’s why I used an HP. The RPN system of data entry made WAY more sense that the parentheses method the TI used, from an engineering point of view.

People would ask me “Why the HP?” I just said “Subsequent calculations, Son.” You start entering the data, and if you discovered you needed to nest the calculations, you just scroll up. If that’s a mistake, you rolled down. You can’t beat that kind of flexibility. TI never got that. Hence the mistakes.

[Crolis]

That’s why I love using my HP 48 GX. Sure it would give you the answers, but you had to work for it, starting with learning RPN number entry.

I think it actually made me better at math. Just reading the user manual was an exercise.