Let the number of pens purchased be n. Then the cost price is 8n. The total expenses incurred would be 8n+W, where W refers to the wage. Then SP in the first case =12×100+11×(n-100) Given profit is 300 in this case: 1200+11n−1100−8n−W=300⇒3n−W=200 In second case: 1200+9n−900−8n−W=−300(Loss)⇒W−n=600 Adding the two equations: 2n=800 n=400 . Thus W=600+400=1000