Question 892127
A woman sold some bags at average cost of $52.when She sold another 4 more bags at average cost of $72, the average cost of all bags become $57. How many bags she sold all?
let she sell X bags 
cost by selling x bags =52x
another 4 bags at average of $72
cost for 4 bags will be =4x72= $288
 total number of bags sell will be  x+4
total cost of sell for 56 bags at average of $57=(x+4)x57
as per given conditions 
52X+288=(x+4).57
52x+288 =57x +228
52x-57x=228-288
-5x=-60
x=12