Solving 6 – 2 + 1 : Think Like Machines?

Recently I have shared the following in my Facebook and it became an interesting discussion. In my next post, I ll post why I have shared it. For the moment will try to solve this !


Simple, right. Can you guess, which is the right answer and the method to achieve the answer?

I say all three methods could beright and so do 3 and 5 answers. But how?

Indeed few posted 3 while some posted 5, the correct answer is 5 (considering pure mathematical approach). But what is the correct method. Both methods, two and three are correct. Not sure?

Even though this is a very simple expression, it seems like many were confused with BODMAS or PEMDAS and mathematics.

BODMAS is the UK standard while PEMDAS is the USA version of it. There are few other variations such as BIDMAS, etc.. Apart from the precedence discussed in mathematics, these rules were developed to make the machines (computers, calculators etc) life easier. In order to feed expressions to machines and get a consistent output. Since their inability to think, we direct the thinking pattern using rules.

Forget any method you have followed, BODMAS or PEMDAS whatever. Will get back to our basics.

6 – 2 + 1 

Then it is possible to write the expression as follow (without changing it’s original meaning);

6 + (1 x -2 ) + 1

Indeed above is equal to

6 + (-2) + 1

Can you identify A + B + C there? Then can you remember the Associative Property?

A + B + C = (A + B) + C = A + (B + C )

Accordingly, do you agree with following?

6 + (-2) + 1 =  6 + [ (-2) + 1 ] =  ( 6 + 1 ) + (-2)


6 – 2 + 1 = 6 + (-2) + 1 = 6 – 1 = 7 – 2 = 5

This is why it says + and – are having equal precedence and calculation should be performed left to right. But it is a simplified version, used to teach machines to solve these expressions. Do not get trapped, use the basics always.

Then, how come 3 would be a right answer. If it is mentioned according to BODMAS the answer is 3, then it is incorrect. But if you design a rule as follow A – B + C = A – (B + C) then according to the assumption the answer is 3. If you check my post, you would see I have not mentioned any assumption or method followed. Therefore it should be in pure mathematical form. So here the most suitable or the correct answer would be 5 and the methods are two and three.

This is why we should always follow the method used to solve a problem rather than focusing the answer alone.

Mathematics is a universal language, so why we need to stick to some rules developed to make the life of the machines easier.


Please add your valuable idea below, will make a discussion, thanks !

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