Someone plans to invest x taka in the bond of 'M' company, which pays 10% interest and y taka in 'N' company bonds, which pay 9% interest. He will invest 9,000 taka require that he receives 850 taka as interest. How much should be invest in each company? (Interest)

প্রশ্নে বলা হচ্ছে, এক লোক ‘M’ কোম্পানিতে 10% সুদে টাকা এবং 'N' কোম্পানিতে 9% সুদে টাকা বিনিয়োগ y করে। সে মোট 9,000 টাকা দুই কোম্পানিতে বিনিয়োগ করে 850 টাকা সুদ হিসেবে নিতে চায়। কোন কোম্পানিতে কত টাকা বিনিয়োগ করবে?

Let, He invested Tk. x in company 'M' at 10%

∴ In 'N' Company, he invested Tk. (9,000-x) at 9%

We know, $I = \frac{P \times r \times n}{100}$

∴ The amount of interest at 10% of Tk. x $= \frac{x \times 10 \times 1}{100} = \frac{x}{10} Tk.$

And the amount of interest at 9% of Tk. (9,000 - x) $= \frac{\left(9000 - x\right) \times 9 \times 1}{100} = \frac{9 \left(9000 -x\right)}{100}Tk.$

According to question $\frac{x}{10} + \frac{9 \left(9000-x\right)}{100} =850$

$$\begin{gathered} \Rightarrow \frac{10x + 81000 -9x}{100}= 850 \\ \Rightarrow x+ 81,000 = = 85000 \\ \Rightarrow x = 85,000 - 81,000 \\ \therefore x = 4, 000 \end{gathered}$$

He will invest 4,000 Tk. in company 'M' and (9,000 - 4,000) = 5,000 Tk. in company 'N'. ans.