All Things in Order

7+7/7+7*7-7=

a) 0

b) 8

c) 50

d) 56

This was a math problem that went around during a recent girl's night out.  Most of the gals kept getting the wrong answer, and couldn't figure out how to get the right answer.  Hint: the answer is NOT d) 56.

You get the incorrect.56 answer if you start at the beginning of the problem and work straight through, from left to right.  7 plus 7 is 14, divided by 7 is 2, plus seven is 9, times 7 is 63, minus 7 is 56.  You did all the work and made it to the end, but it was wrong.

Turns out that the way you do something is just as important - and often even more important - that whether you get to the end or not.

In this case, you have to follow the "order of operations."  The acronym is PEMDAS (even my 10-year-old can quote "Please Excuse My Dear Aunt Sally").  I wonder what dear Aunt Sally did to earn such elementary school notoriety...  You have to approach a math problem in the correct order: Parenthesis, Exponents , Multiplication, Division, Addition, Subtraction.  Actually, the multiply/divide can be done together, as can the add/subtract.

When you follow the correct order, the problem looks different.  7+ 7/7 + 7*7 -7.  Work through the multiply and divide parts of the problem first, the go for the add and subtract.  Same original numbers, but now you get a different answer.  The correct one.

I think I too often try to slog through a problem from left to right without looking at the whole thing and figuring out what the order of operations is.  Whatever is on front of me, that is the part I need to tackle.  But if I step back and figure out what the most important things are, and do those first, then I arrive at a totally different solution.

And it's the right one.

The correct answer is c) 50.  Thanks to my smarty-pants kids who helped me figure it all out completely - and 4 of the 5 got the right answer, too!