Just when I thought I was getting better at math...

[shadowkat]

This

Post by Power 95.3.

made me scratch my head.


7 + 7 divided by 7 +7 x7 -7.

The correct answer is apparently 50.

IF you do it this way: 7+7 =14 divided by 7 =2
2 +7 = 9, 9* 7 =63, 63-7 = 56.

If you do it by calculator = 56

If you do it by Excel = 50

Apparently it is supposed to be 7x7= 49 /7 = 1, then 1+7+7 -7 = 8.
Which still makes no sense. So, it must be = 7x7/7 =1, then 7+7+7 =21 +1
Still makes no sense. I remain puzzled.

This is why I hate math.

Comments

[cactuswatcher.livejournal.com]

This is actually a problem with the folks who made up the problem!

There is an 'order' of arthimetic operations, but unless the person who set up the problem is thoroughly versed in that convention and did the setup perfectly, and the person on the other end (ie you or I) both knows and agrees with their order, the answers all of us will get from the problem will be garbage.

(7+7)/(7+7)*(7-7) is also unfortunately a possible interpretation of the problem as presented. The correct answer to that problem is
(14)/(14)*(0)= 0

Why is this such a mess? Because of the awkward format today's calculators use. I and many others warned those who wanted this format to be standard 30 odd years ago of the nightmares it would create when going beyond the simplest math problems. But it was to no avail because they could type in correctly written algebra problems without thinking. You can't do that with arithmetic problems instead of algebra!

Put simply never try entering a complex arithmetic problem without breaking it down into multiplications and divisions first, because otherwise it will never come out right.
7+(7/7)+(7*7)-7= 7+(1)+(49)-7= 8+42= 50

[beer-good-foamy.livejournal.com]

Yeah, math is tricky that way. Do the calculations in the wrong order and you can end up anywhere...

One of my favourite stumpers:

Three salesmen share a hotel room costing $25/night. The next morning, they each hand the bellboy a $10 note. He runs down to the reception with the $30, gets $5 in change keeps $2 as a tip and hands $1 in change to each salesman.

So each salesman paid $9, times 3 = $27. Plus $2 for the bellboy, making a total of $29.

...Where did the thirtieth dollar go?

[frenchani.livejournal.com]

There should be brackets!

[flake-sake.livejournal.com]

In German we call it the "Punkt vor Strich" rule. It means dots before lines.
So multiplication (.) and division (:) need to be done first, if there are no brackets indicating otherwise. Calculators don't use the rule automatically, excel does.

ETA: Apparently in English the rule is called PEMDAS rule (The letters standing for Powers, exponentials, multioplication, division, addition substraction.

But the order should not matter for the pairs of the same rank (like multiplication and division)and even the calculators get that exponentials and powers are done before the rest (weirdly, since they don't get the devision, multiplication thing).

[spikesjojo.livejournal.com]

PEMDAS (order of operations) - Parentheses then exponents - multiply & divide in order, add and subtract in order.

So that would be 7 divided by 7 = 1
7 x 7 = 49

7+1+49-7 and I get 50.