Try this on windows. Open the calculator app. Now type the following:

100 + 2 * 5

Look at the result. Did it match what you expected?

@VK6VCC while I don't have a Windows instance handy, I'd expect the answer to be 510, rather than 110.

If you use a dumb calculator, you're also going to get 510.

On my RPN calculator I'd type:

100 <Enter> 2 <Enter> 5 x +

@vk6flab that's why RPN rules! 🙂
@VK6VCC If you switch to Scientific mode it should return the correct result IIRC.