Ahmad spent some money on 8 discus and 40 kois. He spent twice as much on the kois. If each discus cost $15 more than each kois, how much did he spend altogether?
Let d = cost of a discus and k = cost of a kois.
40k = 2*8d
d = k+15
So 40k = 2*8*(k+15) or 40k = 16k + 240 or 24k = 240 so k = 10
This means that d = 10+15 = 25
Total spend = $(8*25+40*10) = $600
