For the rodents: Let the number of rodents modified as rats be x. If the genetically modified hamsters must be the minimum possible. For Purple eyes: 50 – 35% of x ≥ 0 50 ≥ 0.35x 142.85 ≥ x If x can be a maximum of 140 (since x must be a multiple of 20), then minimum number of genetically modified hamsters = 1000 – 140 = 860