# Thread: Ratio of 3 things

1. ## Ratio of 3 things

To make FoundaMix concrete I need cement, sand, and aggregate mixed in the ratio 2 : 5 : 7. I need 7 tonnes of concrete for a driveway. How much of each material should I buy?

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2. ## Re: Ratio of 3 things

Originally Posted by joshuaa
To make FoundaMix concrete I need cement, sand, and aggregate mixed in the ratio 2 : 5 : 7. I need 7 tonnes of concrete for a driveway. How much of each material should I buy?

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you have 7 tonnes divided in 2parts + 5 parts + 7 parts = 14 parts (total), 7 tonnes/14 parts =

what would you do next?

dokrbb

3. ## Re: Ratio of 3 things

Joshua

if x = cement ,y = sand z = aggregate then x/2 = y/5 = z/7 then each ratio is equal to (x+y+z)/(2+5+7) = 7000/14 = 500
then x/2 =500 y/5 = 500 z/7 = 500 .......cross multiply to find x,y,z.................1000,2500,3500.............. .......

4. ## Re: Ratio of 3 things

still have no Idea. Please, go on....

5. ## Re: Ratio of 3 things

How did you get the 7000?

6. ## Re: Ratio of 3 things

Originally Posted by joshuaa
still have no Idea. Please, go on....
before going on..., can you tell me what you understood from what I posted, and what means the result you obtain from the fraction I provided you with?

dokrbb

7. ## Re: Ratio of 3 things

Why would I add the parts, then divide the 7 into them? How am I going to benefit from this fraction?

8. ## Re: Ratio of 3 things

Originally Posted by joshuaa
Why would I add the parts, then divide the 7 into them? How am I going to benefit from this fraction?
not 7 but 7 tonnes, so did you?

9. ## Re: Ratio of 3 things

It seems that my Basics of Ratio needs some extra skillS. Even if 7/14 = x/2, 14x = 14, x = 1 which meanS I need 1 tonne of cement, I am still confused of why I add the ratios together, then divide the needed tonnes (7 tonnes) into them!

10. ## Re: Ratio of 3 things

Originally Posted by joshuaa
It seems that my Basics of Ratio needs some extra skillS. Even if 7/14 = x/2, 14x = 14, x = 1 which meanS I need 1 tonne of cement, I am still confused of why I add the ratios together, then divide the needed tonnes (7 tonnes) into them!
look, you have an amount of something (in our case 7 tonnes) which you have to divide in 2 part : 5 part :7 parts, which would be a total of 14 parts of that something,

7/14 = 0,5 (of something - in our case is 0,5 tonnes, or 500kg of something)

now you sum them up proportionally as it is required: (2 parts x 0,5) : (5 parts x 0,5) : (7 parts x 0,5), gives you 1 tonne : 2,5 tonnes : 3,5 tonnes,

do you get now?

dokrbb

11. ## Re: Ratio of 3 things

remember the simple rule that if we want to divide a quantity V in the ratio say a:b:c:d:e etc. then each component is got by dividing the ratio by the sum of the ratios and multiplying it by the quantity. In this case the quantity of component with the ratio b will be [ b/(a+b+c+d+e)] * V
In the given question similarly you can get the quantity of cement = (2/14)*7 Tonnes etc