The easy answer is for him to buy 100 sheep for $1000. But the answer you want is 19 cows × $50.00 = $950.00 1 sheep × $10.00 = 10.00 80 rabbits × $ .50 = 40.00 ------------------------------- 100 animals = $1000.00 I got the answer using number theory. Are you studying number theory? That's a university mathematics course. If so, let me know in the thank-you note and I'll show you how to solve it using number theory, in the topic of linear Diophantine equations. Edwin