Question

A drug loses decayrate percent of its potency every month. Also, a drug is considered expired if it loses more than 50% potency. Your goal is to write a function WhenExpired(decayrate) that returns the number of months after which the drug is considered expired.

Expected Value Notes WhenExpired(4.0) should return 6 16 WhenExpired(0.5) should return 16 1 WhenExpired(55.5) should return 3 When Expired(12) should return 3 | WhenExpired(0) should return 0 WhenExpired(-1.0) should return 0 O WhenExpired(100) should return 0 O WhenExpired(120) should return 0 of the tests

Answer 1

The code is defined as follows:

def WhenExpired(decayrate):
    value = 100.0; #initial value is 100
    months = 0.0;
    decrease = 0.0;
    while value>50.0 and decayrate<100 and decayrate>0: #as per given conditions is decayrate is larger than 100 or decayrate is negetive, no.of. months is zero
        decrease = value * decayrate/100; #the decrease in potency can be computed by multiplying the current value by decayrate
        value = value - decrease; # decrement the value by the decrease amount
        months = months + 1; #increment the number of months for every decrease
    return months #return the months

month = WhenExpired(4);
print("The no.of months = ",month);

to decayexample.py - D:\NMAMIT Nitte Chegg Answers\decayexample.py (3.8.2)* - 0 X Eile Edit Format Run Options Window Help def WhenExpired (decayrate): value = 100.0; #initial value is 100 months = 0.0; decrease = 0.0; while value>50.0 and decayrate<100 and decayrate>0: #as per given conditions decrease = value * decayrate/100; #the decrease in potency can be comput value = value - decrease; # decrement the value by the decrease amount months = months + l; #increment the number of months for every decrease return months #return the months month = WhenExpired (4); print ("The no.of months = ", month);

For Input of 12.0, the output is:

Le Python 3.8.2 Shell - 0 x File Edit Shell Debug Options Window Help Python 3.8.2 (tags/v3.8.2:7b3ab59, Feb 25 2020, 23:03:10) [MSC v.1916 64 bit (AM- D64)] on win32 Type "help", "copyright", "credits" or "license()" for more information. ============ RESTART: D:\NMAMIT Nitte Chegg Answers\decayexample.py ========= The no.of months = 6.0 >>>|

This can be justified with mathematical calculations also.

Initially value = 100

At the end of 1st month, value = 100*(1-12/100) = 88

At the end of 2nd month , value = 88*(1-12/100) = 77.44

At the end of 3rd month , value = 77.44*(1-12/100) = 68.15

At the end of 4th month , value = 68.15*(1-12/100) = 59.97

At the end of 5th month , value = 59.97*(1-12/100) = 52.77

At the end of 6th month , value = 52.77*(1-12/100) = 46.44

At the end of 6th, the value has come below 50% hence the expiry will be after 6 months.

Please do check the values given in the table and revert back in case of any doubts.