Bodmas

Jan 2010
6
0
Hi,

I fully understand the order of BODMAS - It's the order of operations in maths equations.


So lately this little puzzle/riddle has been going around on social media - Solve carefully - 9GAG . I understand that it's a play on grammar because they actually mean 5! as in the factorial.


The thing i notice is that some people argue that the answer is -180 and others argue that it's 120 - for the simple adding and subtracting, not the factorial itself.

25-55+(85+65)
25-55+(150)
25-205
=-180

Others state
25-55+(85+65)
25-55+(150)
-55+150+25
-55+175
=120

Which is correct and why?

Thanks

Ps. I feel quite silly for asking this.
 
Jan 2016
17
4
Ghana
The second one is correct.
25-55+(85+65)
25-55+(150)
To expand a bracket you need to multiply the number inside by the number outside. I.e if it were 1+3+6(2), you'll get 1+3+12.
In this case the number in front of 150, although not obvious, is 1.
25-55+1(150)
It is not shown because 1*150 is the same as 150. With that in mind, expanding the bracket gives:
25-55+150
Which when simplifies to 120 which equals 5!
 
Dec 2015
6
0
Singapore
If this was the question, then the answer would be -180:
25 - ( 55 + 85 + 65 )

But the question says this:
25 - 55 + ( 85 + 65 )

You see, the brackets in the actual question are redundant. They're just there to trip you up. In BODMAS, PEDMAS or whatever you call it, addition and subtraction are on equal grounds. People make the mistake of thinking you should do addition before subtraction, or vice versa. Actually, in a math problem with only addition and subtraction like this, you just work from left to right.

Here's a tip: If the operation directly to the left of the bracket is +, you can ignore the brackets.

Your train of thought should be this:
25 - 55 + 85 + 65
= - 30 + 85 + 65
= 55 + 65
= 120

You needn't feel silly, we all are here to learn and help.
 
Jan 2010
6
0
I realise what they've done that I didn't pick up on. They swapped the sign of 55, which is why it equates to 205 and not 105 like it should be.

Thanks for the advice. And thanks for the tip skunk. I also didn't realise/remember (as I probably got taught that at some stage of life) that addition and subtraction are on the same level.

And I feel silly/embarrassed by this because I've got quite a good engineering degree. :/ Doh! We can't be great at everything I suppose.

I believe that the equations should be done from left to right? Is there a real reason for this or is it just to give people a starting point?
 
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