A man saves Tk 20,000 in 10 years. He saves Tk 200 more every year than the previous year, except the first year. How much does he save in the first year?

Question: A man saves Tk 20,000 in 10 years. He saves Tk 200 more every year than the previous year. How much does he save in the first year?

Solution:
এখানে, সমষ্টি (S_n) = 20000,
পদ সংখ্যা (n) = 10,
এবং সাধারণ অন্তর (d) = 200

সমান্তর ধারার সূত্র অনুযায়ী,
S_n = (n/2) × {2a + (n - 1)d}
⇒ 20000 = (10/2) × {2a + (10 - 1) × 200}
⇒ 20000 = 5 × {2a + 1800}
⇒ 4000 = 2a + 1800
⇒ 2a = 4000 - 1800
⇒ 2a = 2200
⇒ a = 1100

∴ প্রথম বছরের সঞ্চয় = 1,100 Tk