Little Math help? (Easy problem)

[Plaidman]

I'm lousy with math. But I'm trying to reteach my self the basics for my future job. I've gotten my pretests in my books correct for most part, except this one problem.


1 3/5 + 7/8 divided by 1/3

I just can't seem to get the answer, which is suppose to be 4 9/40

can anyone tell me how to get that answer?

[dalesys]

Hint: Divided by a/b is the same as multiplied by b/a.
So one of the steps is to transform from:

1 3/5 + 7/8 divided by 1/3

to:

(1 3/5 + 7/8) multiplied by 3/1

[r2cagle]

Are you just not getting all of the answer right, or part of the answer is not right...

Okay.. simply put... what answer are you getting?

Before you add fractions, the denominators must match. Convert the whole number to a fraction to add, and as Dalesys said to divide by a fraction - is really to invert and multiply.

General rule to work most complex problems is in this order: Add, Subtract, Multiply, Divide.

[Plaidman]

My answers seem to vary -_-.

(1 3/5 + 7/8) multiplied by 3/1 as Dales suggested gave me

1 24/40 35/40 = 59/40 = 2 19/40 then

2 19/40 multip 3/1

99/40 times 3/1

297/40 = 7 17/40

which isnt answer. I'm doing something wrong.

[r2cagle]

Wait... working it out.

You're right == 7 17/40.

Book appears to be wrong.

4 9/40 = 169/40 which is nowhere close to 297/40

***Just go with the fact that you are right***

[Pony_Boy]

this is not an easy problem

but i agree looks like the book is wrong Happens a lot actually

[Pedersen]

1 3/5 + 7/8 divided by 1/3

I just can't seem to get the answer, which is suppose to be 4 9/40

can anyone tell me how to get that answer?

This one really needs the parenthesis to group things properly.

1 3/5 + ((7/8)/(1/3)) is a very different problem from (1 3/5 + 7/8)/(1/3). Put another way:

       7
       -
  3    8
1 - + ---
  5    1
       -
       3

is not the same as:

    3	7
  1 - + -
    5 	8
  -------
     1
     -
     3

The first would be what is indicated with no parentheses. An important mnemonic is "Please Excuse My Dear Aunt Sally". Remember this, and it teaches you the order in which you are supposed to do math.

Please      Excuse    My             Dear     Aunt     Sally
Parenthesis Exponents Multiplication Division Addition Subtraction

Now, all that being said, without any parentheses, the problem should be treated as "take 1 3/5, and add ((7/8) / (1/3))" to it.

A fraction(A) divided by a fraction(B) is equal to A multipled by B, inverted. For this example, (7/8) / (1/3) is the same as saying (7/8) * (3/1). When doing multiplication of fractions, simply multiply top and bottom together. In this case, it becomes 21/8.

7   1   7   3   21
- / - = - * - = --
8   3   8   1   8

Back to the first part: 1 3/5 + 21/8. In order to add fractions where the bottom (denominator) is different, an easy trick is to just multiply the left one (top and bottom) (A) by the right one's (B) denominator, and vice versa. Using this technique, you would be looking at this:

3*8   21*5    24   105   129
--- + ----- = -- + --- = ---
5*8   8*5     40   40    40

Now, see how the 129 is larger than 40? We now reduce the fraction to the minimum we need. 40 goes into 120 3 times, with 9 left over, giving us 3 9/40. Add the original 1 (from the 1 3/5, we used the fraction, but not the 1), and we get 4 9/40.

The final solution is presented below. Every time there's an =, I've moved from one step to another from above.

Hope this helps.

       7
       -
  3    8      3	    7	  1	  3    	7   3	    3	21     24   105	    129		 9     	9
1 - + --- = 1 -	+ ( -  /  - ) = 1 - + ( - * - ) = 1 - + -- = 1 -- + --- = 1 ---	= 1 + 3 -- = 4 --
  5    1      5	    8	  3 	  5 	8   1	    5	 8     40    40	     40  	40     40
       -
       3

[ArcticChicken]

Order of operations. Perentheses, exponents, multiply/divide, add/subtract.

You have to divide 7/8 by 1/3 BEFORE you add 1 3/5.

You start with
1 3/5 + 7/8 divided by 1/3

7/8 divided by 1/3 = 2 5/8

So the problem becomes
1 3/5 + 2 5/8

multiply 3/5 by 8/8, and 5/8 by 5/5, to get 24/40 and 25/40 respectively.

1 24/40 + 2 25/40 = 3 49/40 = 4 9/40

[r2cagle]

AHHH... see... without parenthesis it does make a different answer...

Plaid... watch those parentheses

And how did you guys figure out that it was missing those?

[Mel]

When I was re-taking grade 12 math for a college course, I found quite a few wrong answers in the answer book. It does happen a lot.

[Plaidman]

I swear the book didnt have any parenthesis on that problem. It was just straight

1 3/5 PLUS 7/8 divided by 1/3. No parenthesis. All the fractions were in the fraction symbol which I can't do on my comp, and the divided symbol was /

In anycase thank you so much everyone, especally Pedersen and Artic for writing it all down step by step, and thanks to r2cagle for trying alot too.


I also see what I was doing wrong on a few of them, because for some stupid reason I was treating the times by doing 7/8 divided by 1/3 as 7/8 times 3/1 on some.

But I got the answer, and learned again. I feel like an idiot it's been so long, but thank you. I might have to take calcaus next term, so I'm racing to catch up.

[Pedersen]

That's okay, and can even be expected. That's why I said parentheses are needed. They make that problem much clearer.

However, if you don't have any parentheses, then all you can do is fall back on the mnemonic I mentioned "Please Excuse My Dear Aunt Sally". Follow through on each of those operations in that order. Parentheses first, then exponents, then multiplication, then division, then addition, then subtraction. You'll get the right answer by doing that.

[r2cagle]

I swear the book didnt have any parenthesis on that problem. It was just straight

I used to battle with my teachers whenever the book was wrong.

[ArcticChicken]

I swear the book didnt have any parenthesis on that problem. It was just straight

1 3/5 PLUS 7/8 divided by 1/3. No parenthesis. All the fractions were in the fraction symbol which I can't do on my comp, and the divided symbol was /

NOT having parenthesis is why the problem comes out as 4 9/40.

The order of operations is the order you do a problem in. First you do anything that's inside parenthesis, then you do any exponents (squared, cubed, etc.), then multiplication and division, lastly you do addition and subtraction.

As for how I knew that there were no parenthesis in the original problem, one of the most common mistakes is in the order of operations.

[tollbaby]

Plaid, I feel for you, man....

The math, it burns us!