Mature student back to basics

[micky95]

Hi

I'm revisiting my GCSEs in my 40s and I'm doing okay, but there's one question I can't get my head around;

18-10÷5+3²

My calculator says 25, but I'm baffled how you work this out in your head.
Any help would be much appreciated.

 

[blamocur]

My calculator says 25, but I'm baffled how you work this out in your head.

One operation at a time? What is 10/5 ? How about [imath]3^2[/imath] ?

 

[Dr.Peterson]

Hi

I'm revisiting my GCSEs in my 40s and I'm doing okay, but there's one question I can't get my head around;

18-10÷5+3²

My calculator says 25, but I'm baffled how you work this out in your head.
Any help would be much appreciated.

Here's an introduction to the ideas involved:

Order of Operations - PEMDAS

Learn how to calculate things in the correct order. Calculate them in the wrong order, and you can get a wrong answer!

www.mathsisfun.com

Or this, which is similar but uses more British than American terms:

Order of Operations - BODMAS

Learn how to calculate things in the correct order. Calculate them in the wrong order, and you can get a wrong answer!

www.mathsisfun.com

 

[Steven G]

Before you add or subtract you must know what you are adding or subtracting.
18-10÷5+3² means (18)-(10÷5)+(3²) = 18-2+9.

 

[The Highlander]

18-10÷5+3²
My calculator says 25, but I'm baffled how you work this out in your head.
Any help would be much appreciated.

What is your problem? Why are you "baffled"?

When you attempt work it out in your head are you thinking:-

"18 - 10 = 8, then 8 ÷ 5 is the same as 16 ÷ 10 = 1.6 and 1.6 + 9 (3²) = 10.6" (or similar)?

You're getting 25 as the answer because that is the correct answer that will be produced by any half decent ('scientific') calculator that is obeying the rules of correct Order of operations (see also the links already referred to above).

Some (cheap?) basic calculators might well give you 10.6 as the answer if you enter the sum just as it's written because they carry out each operation just as it is entered (like I illustrated above) and not in the correct order (that a good scientific calculator would).

If you Google "BBC Bitesize BODMAS" you will get lots of links to more explanations of this issue. This particular page is aimed directly at GCSE students.

Hope that helps.