Expert: Richard J. Raridon - 3/25/2007

Question
hi richard please will you be able to help with the following question
An order for 2500 facing bricks and 300 insulation blocks cost £840.Another order was made for 1500 facing bricks, but 100 of the insulation blocks were faulty and had to be returned. The total value of the second invoice,including a refund for the faulty blocks, was £420.calculate the cost of the facing bricks per 1000 and the cost of insulation blocks per m^2, given that there are 10 blocks/m^2.
my simultanious equastions that i took are
2500x + 300y = £840
1500x + -100y = £420
ive tried to work this out but cant get the right answer
will you be able to show me how to factorise it and also the method called ilimination
regards simon

Answer
First of all, leave of the pound sign in the equations.  From the equations you gave, both x and y are 0.30.  
So that makes the cost of bricks per thousand = 300 and the blocks per m^2 as 3.  However, are you sure you stated the problem correctly?  Did the second order have more than 100 blocks and 100 were returned?