Copier D prints at a rate of 90 letters in every 5 minutes and Copier E prints at a rate of 126 letters in every 6 minutes. At 7 p.m., both copiers started printing. After a while, Copier D stopped printing for some time as the ink cartridges were being changed before it continued to print again. Copier E continued printing during this time. At 9 p.m., the total number of letters printed during the past two hours was 5109. Express the number of letters printed by Copier D 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 D prints per min = 90 ÷ 5 = 18
Number of letters Copier E prints per min = 126 ÷ 6 = 21

From 7 p.m. to 9 p.m. = 2 h
1 h = 60 min
2 h = 120 min

Number of letters printed by Copier E in 7 h
= 120 x 21
= 2520

Number of letters printed by Copier D in 7 h
= 5109 - 2520
= 2589

Percentage of the number of letters that Copier D printed over the total number of letters printed
= ²⁵⁸⁹₅₁₀₉ x 100%
≈ 50.68%

Answer(s): 50.68%