Answer:
3.75 hours
Step-by-step explanation:
Bob completes his homework in 2.5 hours.
In 1 hour, he completes 1/2.5 of his homework.
Joe completes his homework in x hours.
In 1 hour, he completes 1/x of his homework.
Together, they complete the homework in 1.5 hours.
In 1 hour, they do 1/1.5 of the homework.
1/2.5 + 1/x = 1/1.5
Convert the decimal numbers in the numerators into fractions.
1/(5/2) + 1/x = 1/(3/2)
2/5 + 1/x = 2/3
Multiply both sides by the LCD, 15x.
6x + 15 = 10x
-4x = -15
x = 3.75
Answer: 3.75 hours
