Am I correct or is Wolfram correct?

[uperkurk]

4/5t + 7 = 47

I say

4/5t = 40

t = 50

but wolfram says t = 1/50

Sorry I have to learn how to use latex again -_-

 

[berkeman]

4/5t + 7 = 47

I say

4/5t = 40

t = 50

but wolfram says t = 1/50

Sorry I have to learn how to use latex again -_-

You need to add quotes to make it what you want: (4/5)t + 7 = 47

Wolfram thinks you want it to be (4/5t) + 7 = 47

 

[jbriggs444]

I think the delta is whether 4/5t = 40 is interpreted as 4/(5t) = 40 or (4/5)t = 40

The standard convention is that multiplication and division bind equally tightly even when multiplication is indicated by juxtaposition and that both are left-associative. That means the latter interpretation is conventional. Barring some typography that OP has not copied carefully, OP is correct and Wolfram is in error.

 

[SteamKing]

Add parentheses (), not quotes " ".

 

[Bill Simpson]

This

http://www.wolframalpha.com/input/?i=solve+4/5t+++7+=+47+for+t

shows in 2D typset notation what WolframAlpha thinks 4/5t + 7 = 47 is.

(which surprised me a little)

Now "correctness" I'm not even going to try to get into.

 

[pwsnafu]

Mathematica is sensitive to spaces. It doesn't have much choice as it needs to be able to distinguish between "xy" and "x y" (the former is a variable with name xy while the latter is the product of two variables x and y).

Same thing here: if you type "4/5 t" (with the space) it'll be parsed as $\frac{4t}{5}$.

 

[Serinety]

The obvious part of this discussion as it relates to OP, make sure to look at the input interpretation when you enter formulas. Wolfram clearly displays how it interprets your input, if it does not match your equation then the answer will not match either. logic 101

 

[rollingstein]

I think the delta is whether 4/5t = 40 is interpreted as 4/(5t) = 40 or (4/5)t = 40

The standard convention is that multiplication and division bind equally tightly even when multiplication is indicated by juxtaposition and that both are left-associative. That means the latter interpretation is conventional.

Yes, but only when multiplication is explicitly indicated.

e.g.Even wolfram uses the convention if told 4/5*t

For implied multiplications I'm with Wolfram. Implied multiplications ought to bind tightest as a convention; that makes intuitive sense to me.

 

[jbriggs444]

Ahh, sensible. That case did not come up when learning parsing rules in comp sci -- we never used juxtaposition to denote multiplication.

 

[rollingstein]

Ahh, sensible. That case did not come up when learning parsing rules in comp sci -- we never used juxtaposition to denote multiplication.

Right. Most modern programming languages would throw an error for doing an implied multiplication.

Come to think of it, which other languages allow something like 5t instead of 5*t?

 

[Serinety]

[QUOTstein;4246799]Right. Most modern programming languages would throw an error for doing an implied multiplication.

Come to think of it, which other languages allow something like 5t instead of 5*t?[/QUOTE]

As far as languages go, I don't think any would interpret 5t ad 5*t .

Wolfram does do implied multiplication and will interpret 5t as the product of the 2. The problem here is the 5t being in the denominator.

If we expected wolfram to interpret 4/5t as (4/5)*t , then we would have to make a concession for the case of 4/(5t) by use of brackets.

In either case, 4/5t is ambiguous when written line style so brackets are required for clarification.

 

[Bill Simpson]

Wiki weighs in
http://en.wikipedia.org/wiki/Order_of_operations#Exceptions_to_the_standard

TI weighs in
http://epsstore.ti.com/OA_HTML/csksxvm.jsp?nSetId=103110

but I still can't track down any obscure programming language that supports implied multiplication.