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 application of lenear equation
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ren
New Member

USA
1 Posts

Posted - 09/10/2007 :  13:41:40  Show Profile
In a certain concrete mix there was four times as much gravel as cement. The total volume of gravel and cement in the mix was 22.5 ft. How much of each was in the mix?

the answer is 18 and 4.5
Please explain in terms of pairs of lenear equation.
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the_hill1962
Advanced Member

USA
1468 Posts

Posted - 09/10/2007 :  14:03:58  Show Profile
Let c=amount of cement
and g=amount of gravel
So, "four times as much gravel as cement" means g=4c (how do you figure that the equation is g=4c ??? --- because there was more gravel, you multiply the amount of cement by 4).
The other equation is easy to get, "total volume is 22.5" means c+g=22.5
You can substitute "4c" for "g" into the cg=22.5 since g=4c.
See how it works------c+g=22.5 becomes c+4c=22.5
Now that simplifies to 5c=22.5 which means c=4.5
and since g=4c, g=44.5=18. Of course you need to indicate the unit

Edited by - the_hill1962 on 09/10/2007 14:11:11
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