Order of operations, BODMAS.

Question

Given the following expression:

-7 + 1 - 8 * -10 / 28 - 67 + -54

I resolve it thus:

-7 + 1 - -80 / 28 - 67 + -54

-7 + 1 - -2 - 67 + -54

-6 - -2 - 67 + -54

-4 - 67 + -54

-71 + -54

-125

However various online calculators say the answer is:

-124.14285714285714

What am doing wrong?

Dirac'stwin · Answer 1 · 2017-07-28T14:50:32.570

1

The main issue here is in the second line where you simplify $-80/28$ to equal $-2$. In fact, (-80/28) = (-20/7). So the resulting sum simplifies to $-127 + 20/7$ which does in fact expand to -124.1428...

Fluff aside, I think the real problem here is you're confusing $8$ with $0$ on whatever device you are using. Although if that were true then how come you typed 80 correctly?

edited Jul 28 '17 at 14:50

answered Jul 28 '17 at 14:14

Dirac'stwin

51

It should be: -80 / 28 = -2 – tuk Jul 28 '17 at 14:35
The point is $\pm\frac {80}{28} \neq \pm 2$ – amWhy Jul 28 '17 at 14:39
if it is a troll, its a very good one – jg mr chapb Sep 12 '17 at 01:54

score 0 · Answer 2 · answered Jul 28 '17 at 17:16

-80 / 28 = -2.857142857142857

Not the -2 stated in question working.
Changing this value now gives the same final result as the online calculators:

-124.14285714285714

Note: My code was casting the: -2.857142857142857 to an integer(not a double): -2

So losing: -0.857142857142857 on the conversion.

Order of operations, BODMAS.

-124.14285714285714

2 Answers2