Math
posted by Kyle
A contractor requires a cement mix that is 70% sand and 30% cement.
He has 700 kg of a cement mix that is 80% sand and 20% cement.
How much cement should he add so that he gets the required mix?
My set up:
required mix = (S)(.7) + (C)(3)
700kg = (S)(.8) + (C+X)(.2)
Is this even correct?

Henry
C / (S+c) = 0.3.
C = 0.8 * 700kg = 560kg.
C / (560+C) = 0.3,
C = 168 + .3C,
C  0.3C = 168,
0.7C = 168,
C = 240kg.
Respond to this Question
Similar Questions

Algebra
A batch of concrete is made by mixing 1 part cement, 2.5 parts sand, and 3.5 parts gravel. How many pounds of sand and gravel are needed to make 300 pounds of cement? 
Math,Ratio
mr kim mixes cement&sand to make a mixture.he uses 2 pails of cement for every 5 pails of sand. a) if he uses 24 pails of cement,how many pails of sand does he use? 
Maths
Sam used cement and sand to prepare a mixture. The ratio of the number of pails of cement used to the number of pails of sand used was 1:2. Sam then added 8 more pails of cement and the ratio became 5:2. A.) How many pails of cement … 
Math
A contractor has been asked to pave 15 miles of new road. Before he can set his price, he needs to know how much the cement will cost. If the road is 45 feet wide and 9 inches thick and the cost of cement is $35 per cubic yard, what … 
math((PLEASE HELP!))
A contractor has been asked to pave 15 miles of new road. Before he can set his price, he needs to know how much the cement will cost. If the road is 45 feet wide and 9 inches thick and the cost of cement is $35 per cubic yard, what … 
Algebra 1
You are making up your own mix of concrete to patch a set of stairs. In order to have the proper mix, you need to mix 1 part of Portland cement with 2 parts of sand and 3 parts of gravel. A. How many total parts are in one batch of … 
Math
Mr Kim mix cement and sand to make a mixture.He uses 2 pails of cement for every 5 pails of sand. (A) Find the ratio of the number of pails of cement to the number of pails of sand. (B) If he uses 24 pails of cement,how many pails … 
Math
concrete is to be mixed using cement and sand into the ratio 2:5. how much sand will be required to mix with 96 pounds of cement? 
Maths
Matilda is looking at making a concrete mix. She mixes 2 parts of cement powder to every 7 parts of sand. Cement costs 35 cents a kilogram and sand costs 20 cents a kilogram. In total she spent $180. What was the total weight of cement … 
mathematical literacy
Brick layers makes mortal with cement lime sand and water in the ratio of 1:1:5:1 if they have 2bucket of lime, how much should they use for cement, sand and water?