Answer:
Paula = 4 hours
Roberto = 12 hours
Step-by-step explanation:
Time taken by Paula = x
Time taken by Roberto = x +. 8
Paula's rate = 1/x
Roberto's rate = 1/(x + 8)
Combined rate = 1/3
Time it takes each if them working alone ;
Paula's rate + Roberto's rate = combined rate
1 /x + 1 / (x +8) = 1/3
Take the L. C. M
((x+8) + x) / x(x+8) = 1/3
(2x + 8) / x(x + 8) = 1/3
3(2x + 8) = x(x + 8)
6x + 24 = x² + 8x
x² + 8x - 6x - 24 = 0
x² + 2x - 24 = 0
Solving the quadratic equation :
x² + 6x - 4x - 24 = 0
x(x + 6) - 4(x + 6) = 0
(x - 4) = 0 or (x + 6) = 0
x = 4 or x = - 6
Time taken cannot be negative
Hence, x = 4
Hence, working alone, it takes ;
Time taken by Paula = 4
Time taken by Roberto = 4 + 8 = 12
