Answer: a) 15 b)
Step-by-step explanation:
Let X be the number of days:
a)
For LESSONS:
Jordan does 10 / day ( 10*X)
Marco 5 / day ( 5*X)
Junyi 5 / day ( 5*X)
For TESTS:
Jordan does 5 / day ( 5*X)
Marco 10 / day ( 10*X)
Junyi 8 / day ( 8*X)
for each they need a total of 300
a) days for the lessons
b) days for the tests
so they need 15 days to finish both tasks
now if Junyi gets sick we just eliminate his contribution
a) days for the lessons
b) days for the tests
so in 20 days they will finish without him
If jordan works 10 hours a day, we just replace him with 10/24
a) days for the lessons
b) days for the tests
so at the end to complete both tasks they need 29.58 days