calculate annualised return R on financial investment that has returned 11% over 28 monthly investements of $1

moneyh.py

import numpy as np
from scipy.optimize import minimize_scalar

def moneyh(R):
  """ save 1$ every month for 28 month

  Args:
    R: annualised yearly interest rate

  Returns:
    how much you have at the end of 28 month
  """
  moneys = np.sum([np.exp(R*t/12) for t in range(0, 28)])
  return moneys

def loss(R):
  """ minimise loss, semi got 11% return
  """
  return np.power(moneyh(R)-1.11*28, 2)

res = minimize_scalar(loss)
# >>> res.x
# 0.091093940594436429