Could anyone please help me to calculate the Rate of Interest of the
Following?

Problem 1:

Intestment Rs. 4384 for Next 20 years. ie Total Investment Rs. 87680

Maturity at the end of 25th year.

Maturity Value = Rs. 265500

I have calculated the Rate of Interest (ROI) as follows:

=ROUND(((265500-87680)/87680*(365/(25*365)))*100,2) ie 8.11%

Problem 2:

Intestment Rs. 6450 for Next 20 years. ie Total Investment Rs. 129000

Maturity at the end of 20th year.

Maturity Received Such as follows:

at the end of 5th year = Rs. 20000

at the end of 10th year = Rs. 20000

at the end of 15th year = Rs. 20000

at the end of 20th year = Rs. 40000

plus interest = Rs. 84000

Total : 184000

I have calculated the Rate of Interest (ROI) as follows:

=ROUND(((184000-129000)/129000*(365/(20*365)))*100,2) ie 2.13%

Is the both procedure of calculation right?

May I know the correct function for solution?

Thanks in advance.

Regards