The compound interest of a sum in 8 years is Rs. 400 and compound interest of same sum in 16 years become Rs. 1000. Find the compound interest on same sum of money in 20 years. किसी मूलधन का 8 वर्षों की चक्रवृद्धि ब्याज 400 रू है तथा 16 वर्षों का चक्रवृद्धि ब्याज 1000 रू है । तो 20 वर्षों का चक्रवृद्धि ब्याज ज्ञात कीजिए।