By selling 5 articles at Rs. 840 a shopkeeper gives 2 articles as commission and got 20% profit. Find the cost price of 1 article? एक दुकानदार 5 वस्तुएं 840 रू. में बेचता है तथा 2 वस्तुएं कमीशन के रूप में दे देता है और उसे 20% का लाभ होता है तो एक वस्तु का क्रयमूल्य ज्ञात कीजिए।

Effective selling = 5 - 2 = 3 articles for Rs. 840. With 20% profit: SP = 1.2 × CP_total, so 840 = 1.2 × CP_total, giving CP_total = 700. This is CP of 5 articles, so CP of 1 article = 700/5 = 140. But wait - the commission means only 3 articles are effectively sold. So CP of 3 = 700, CP of 1 = 700/3 = 233.33? No. Let's reconsider: SP of 5 = 840, 2 given free, so effective SP of 3 = 840. With 20% profit on 5 articles: CP_5 × 1.2 = 840, CP_5 = 700, CP_1 = 140. Wait, but if 2 are free... Actually: Selling 5 for 840, giving 2 free means customer pays 840 for 3 articles effectively. But shopkeeper's cost is for 5 articles. Profit is on cost of 5. 840 = 1.2 × CP_5, so CP_5 = 700, CP_1 = 100.