Copier Y prints at a rate of 90 letters in every 3 minutes and Copier Z prints at a rate of 135 letters in every 5 minutes. At 4 p.m., both copiers started printing. After a while, Copier Y stopped printing for some time as the ink cartridges were being changed before it continued to print again. Copier Z continued printing during this time. At 6 p.m., the total number of letters printed during the past two hours was 7078. Express the number of letters printed by Copier Y as a percentage of the total number of letters printed by both copiers. Round off your answer to 2 decimal places.
Number of letters Copier Y prints per min = 90 ÷ 3 = 30
Number of letters Copier Z prints per min = 135 ÷ 5 = 27

From 4 p.m. to 6 p.m. = 2 h
1 h = 60 min
2 h = 120 min

Number of letters printed by Copier Z in 4 h
= 120 x 27
= 3240

Number of letters printed by Copier Y in 4 h
= 7078 - 3240
= 3838

Percentage of the number of letters that Copier Y printed over the total number of letters printed
= ³⁸³⁸₇₀₇₈ x 100%
≈ 54.22%

Answer(s): 54.22%