Three printing presses, R, S, and T, working together at their respective constant rates, can do a certain printing job in 4 hours. S and T, working together at their respective constant rates, can do the same job in 5 hours. How many hours would it take R, working alone at its constant rate, to do the same job?

A. 8
B. 10
C. 12
D. 15
E. 20

20(E)

Step-by-step explanation:

Printing press R, S and T are working together at their respective constant rate.

They can do a job for 4 hours.

Let r, s and t be the time for printing press R, S and T to complete the job alone at their respective constant rate.

Rate of printing press R = 1/r

Rate of printing press S = 1/s

Rate of printing press T = 1/t

Rate = job / time

R + S + T = 4

1/r + 1/s + 1/t = 1/4

S + T = 5

1/s + 1/t = 1/5

Substitute 1/s + 1/t = 1/5 in the equation 1/r + 1/s + 1/t = 1/4

1/r + 1/5 = 1/4

1/r = 1/4 - 1/5

1/r = (5 - 4)/ 20

1/r = 1/20

r = 20 hours

It takes the printing press R 20 hours to complete the job alone

relating to or denoting a system of numbers and arithmetic based on the number ten, tenth parts, and powers of ten.

step-by-step explanation:

the multiples of 15 are 15, 30,45, 60, 75, 90, 105, 120, 135, 150, 165, 180, 195,   210, 225, 240, 255, 270, 285, 300, 315, 330, 345, 360, 375,   390, 405, 420, 435, 450, 465, 480, 495, 510, 525, 540, 555, 570, 585, 600, 615, 630, 645, 660, 675, 690, 705, 720, and 735.

the factors of 15 are 1, 3, 5, and 15.

hope that , fam!

-une, your fren : )