Basic maths - Quantity surveyors

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GoneFishing111 25 Nov 2018

Mature student here, not done any maths since school, currently doing a report for my degree and im struggling with some basic maths, im trying to break down a total figure for labour but it doesn't look right.

Quote amount of £150500, split 60:40, Labour:Materials, i get the labour to £90300.00.

So, total cost of labour, broken into a ratio 10:5, (crafts persons:general operatives) gives costs of £60200.00 and £30100.00 respectively.

When you divide the above figures by the hourly rates paid (£19.98 & £15.16) you get 3013 total hours for crafts ops and 1922 total hours for gen ops, which doesn't fit the 10:5 ratio?

Or should it? Or is my maths wildly inaccurate? Good job im doing building surveying and not QS. 

Wont see my lecturer for a few days, thought this might catch the eye of someone competent!

 

In reply to GoneFishing111:

I've not checked your ratio sums but the hours are not going to be in the same ratio as the costs - they can't be.  If you start out with cost numbers in the ration 10:5 and then you divide each side by a different hourly rate then the ratio of the hours isn't going to be 10:5.

GoneFishing111 25 Nov 2018
In reply to tom_in_edinburgh:

Im sure you are right, but im still clueless.

EDIT: yes of course you are right, the division by the different hourly rates makes it impossible.

In my mind the craft ops hours should be twice that of the gen ops, because there's twice as many of them?

 

 

Post edited at 23:03
 Lurking Dave 26 Nov 2018
In reply to GoneFishing111:

Nah not wildly inaccurate. 

Craft hours = 60,200/19.98= 3,130 hours

General = 30,100/15.16= 1,986 hours

It should't fit the 10:5 ratio as the cost per hour is different for the different trades.

LD

 Wainers44 26 Nov 2018
In reply to GoneFishing111:

The question looks like it's driving at the classic 2 and 1 gang, ie a labourer servicing 2 craftsmen.

So working out the proportions by cost isn't right if their unit rates are different. 

The question isn't thought  through though as they can't be proportional by cost and time (same proportion) if the rate is different. 

ceri 26 Nov 2018
In reply to GoneFishing111:

Is the question supposed to be " split the money so you have 2 crafts and one general person, taking into account their different hourly rstes"? In which case the money for the crafts people will be more than 2/3?

 stevieb 26 Nov 2018
In reply to GoneFishing111:

So, total cost of labour, broken into a ratio 10:5, (crafts persons:general operatives) gives costs of £60200.00 and £30100.00 respectively.

When you divide the above figures by the hourly rates paid (£19.98 & £15.16) you get 3013 total hours for crafts ops and 1922 total hours for gen ops, which doesn't fit the 10:5 ratio?

The answer depends on what the exact question is. If the costs need to be divided 10:5, then you've got it. If, on the other hand, a working team is in the ratio 10:5, then you should calculate the cost of a team (2 craft + 1 gen = £55.12) and divide your labour costs by this.

GoneFishing111 26 Nov 2018
In reply to stevieb:

Hi guys, there is no question as such, its an assignment with very limited detail, we have to make up a total price for a tender for a client, inclusive of domestic sub-contractor prices (one of, which is what this post is about).

Im trying to be clever that's all, the subbies have requested a mixer as they are plasterers to be supplied by the main contractor as an attendance item. There are no other details supplied.

Im trying to break down their price, into labour/materials and applying our main contractor rates plus a percentage addition and assuming the amount of men they will deploy for the task.

If i can figure this out, which i think i nearly have i can then calculate the time taken to do the job and thus the amount of time the main contractor (me) will need to hire a mixer for to fulfil the attendance.

I tried pushing it in to preliminaries but she didn't like that, she wants to see our analytical skills.

In lieu of missing information she wants us to make "justified assumptions".

Daniel.

Post edited at 09:41
 stevieb 26 Nov 2018
In reply to GoneFishing111:

It’s not my area of business, but my assumption would be that the 10:5 ratio is more likely to be for hours worked, rather than cost. 

 

 jkarran 26 Nov 2018
In reply to stevieb:

> It’s not my area of business, but my assumption would be that the 10:5 ratio is more likely to be for hours worked, rather than cost. 

10:5 seems a strange way of specifying something unless the 10 and 5 relate to something with obvious human meaning otherwise you'd surely simplify the ratio to 2:1. Or perhaps its just an exercise in working with ratios.

OP: your 1922 hours looks wrong, perhaps a typo? 30100/15.16=1985

jk

GoneFishing111 26 Nov 2018
In reply to jkarran:

The 10:5 refer to the 10 crafts persons and 5 general opertives, 2:1 would be simpler, agreed.

Sorry it should read £15.66!

stevie b - hours worked is what im trying to get at, but with no other information other than their "all in price" i cant see any other way of doing it.

Post edited at 12:25
 krikoman 26 Nov 2018
In reply to GoneFishing111:

I think you might need to tie down the problem if you got a split in costs Skilled v Labour, then it's the costs that are ratioed not the hours.

Supposing skilled got £1000/hour and labour got £10, a 50/50 split on costs of £2000 would mean you get 1 hours skilled and 100 hours labour, obviously the ration don't hold for the amount of hours.

 galpinos 26 Nov 2018
In reply to GoneFishing111:

Labour cost: £90300

”Team” cost per hr.: £55.62

Divide labour cost by team cost gives your “team hrs”, multiply by 3 and you get total manhours. You can break that back down into Craft and general hours (2:1 ratio) and then total craft and general labour costs)

1624 "Team" Hrs

4870 Total Hrs

3247 Craft Hrs

1624 General Hrs

£64875 Craft Cost

£25424 Labour Cost

(Apologies for rounding)

To just work out the length of duration for the mixer, use the "team hours" total and the maximum number of gangs your workfaces permit.

Post edited at 14:42
 stevieb 26 Nov 2018
In reply to GoneFishing111:

Yes, then if you need to split the hours worked on a 10:5 (or 2:1) ratio. Then calculate the cost of your ‘team’ and divide the Quote (90300) by this number (2x19.98 + 1x15.66). This will give you the number of ‘team hours’. Then double the team to get the number of crafts persons. 

This assumes you don’t need to include profit, contingency etc

GoneFishing111 26 Nov 2018
In reply to galpinos:

Cheers everyone, the grouping makes it much easier. 

Thanks again!


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