[USER (data scientist)]: Thanks! Now, how about the approval rates for the age group 40-59? Please calculate and display the approval rates for the middle-aged group (ages 41 to 58) in the 'credit_customers' dataset.
My template of code snippet is:

---BEGIN CODE TEMPLATE---

import pandas as pd 
import pickle
from decision_company import read_csv_file, 

# please import the necessary private functions from decision_company first
 
# Load the dataset 
credit_customers = read_csv_file("credit_customers.csv") 
 
# YOUR SOLUTION BEGIN:
<code1>
[COMPLETE YOUR CODE] 
</code1>
# YOUR SOLUTION END

print(approval_rates_middle_age)

# save data
pickle.dump(approval_rates_middle_age,open("./pred_result/approval_rates_middle_age.pkl","wb"))

---END CODE TEMPLATE---

[YOU (AI assistant)]: No problem! Here's the code to calculate approval rates for the age group 40-59:
'''
import pandas as pd 
import pickle
from decision_company import read_csv_file, 

# please import the necessary private functions from decision_company first
 
# Load the dataset 
credit_customers = read_csv_file("credit_customers.csv") 
 
# YOUR SOLUTION BEGIN:
