noob .... can't read formula !

[Mhoppy2018]

Hi All,
I've been given this formula at work with an example answer and try as I might I can't multiple in the correct order to get to the right answer. Ideally I'm trying to recreate in Excel, but i'd like to understand and step through it first.

Can anyone help ?

 

[Dr.Peterson]

Hi All,
I've been given this formula at work with an example answer and try as I might I can't multiple in the correct order to get to the right answer. Ideally I'm trying to recreate in Excel, but i'd like to understand and step through it first.

Can anyone help ?

It's written a little oddly, but makes sense. I can show you how to do it in Excel, but since you want to understand it first, the best way to start will be for you to show us what you have done, and what result you got. That way, we can see if you are making any mistakes, and reassure you where you are right.

In fact, I got a different value than they did. I just tried once, and may have made a mistake or two; but if you got the same result, maybe we're actually right!

 

[Deleted member 4993]

I got a different answer too ....

 

[mmm4444bot]

The image is low-quality. With browser zoom, I see the following.


\(\displaystyle J_{yd} = \dfrac{w \cdot \big( \frac{d}{2} \big) \cdot H^{4}}{1920 \cdot E_{al} \cdot f} \cdot 10^{8} \cdot \Bigg( 25 - 40 \cdot \dfrac{\big( \frac{d}{2} \big)^{2}}{H^2} + 16 \cdot \dfrac{\big( \frac{d}{2} \big)^{4}}{H^{4}} \Bigg) \; \text{cm}^{4}\)


I get J_yd = 115.0721 cm⁴ (rounded) using these values:

w = 120

d = 2.8

H = 3

E_al = 7 000 000 000

f = 0.015


In the given formula, we can make some cancellations between constants; it then becomes:


\(\displaystyle J_{yd} = \dfrac{78125}{3} \cdot \dfrac{w \cdot d \cdot H^{4}}{E_{al} \cdot f} \cdot \Bigg(25 - 10 \cdot \bigg( \mkern-4mu \dfrac{d}{H} \mkern-4mu \bigg)^{\mkern-6mu 2} + \bigg( \mkern-4mu \dfrac{d}{H} \mkern-4mu \bigg)^{\mkern-6mu 4} \; \Bigg) \; \text{cm}^{4}\)

 

[Mhoppy2018]

Thanks All, more info as requested.

I get the same answer as mmm4444bot, so i'm confused I've attached my workings and the original document. I either missing something obvious or this document is wrong. Very frustrating.

I'm not confident enough with the math language to be sure either way.

Thanks in advance.

 

[mmm4444bot]

… I either missing something obvious or this document is wrong …

There's error somewhere in the document (eg: typographical, mathematical, measurements).

Their results for J_yc and J_yd don't jive with the rest of the information.

I can see they're a bit sloppy. They performed the same calculation twice; first they rounded J_yc to 58.65 and then J_yd to 58.7

When they added these results, they wrote 58.65+58.6=117.3

So, they rounded up from 117.25 when they ought to have rounded up from 117.35

Finally, at the very bottom, they report the number 121.9 :-?

 

[Mhoppy2018]

Thankyou, Thankyou, Thankyou.

There's error somewhere in the document (eg: typographical, mathematical, measurements).

Their results for J_yc and J_yd don't jive with the rest of the information.

Thanks mmm4444bot for the confirmation, looks like I've gone down a blind alley on finding a solution.
I was beginning to doubt my sanity last night (many already have).

Back to the drawing board !