Question 110945
s+b+m=20 ... 4s+.5b+.25m=20 ... 3=s ... 1<=b<=16 ... 1<=m<=16


the cost of the Siamese helps to narrow the possibilities
... if she buys less than 3 Siamese, then there is too much money remaining to keep the number of fish at 20
... if she buys more than 3 Siamese, then there is not enough money to get the number AND variety of fish necessary


b+m=17 ... .5b+.25m=8 ... .5(17-m)+.25m=8 ... 8.5-.5m+.25m=8 ... -.25m=-.5 ... m=2 ... so b=15