Copier Z prints at a rate of 90 letters in every 2 minutes and Copier A prints at a rate of 126 letters in every 6 minutes. At 4 p.m., both copiers started printing. After a while, Copier Z stopped printing for some time as the ink cartridges were being changed before it continued to print again. Copier A continued printing during this time. At 6 p.m., the total number of letters printed during the past two hours was 6918. Express the number of letters printed by Copier Z 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 Z prints per min = 90 ÷ 2 = 45
Number of letters Copier A prints per min = 126 ÷ 6 = 21

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

Number of letters printed by Copier A in 4 h
= 120 x 21
= 2520

Number of letters printed by Copier Z in 4 h
= 6918 - 2520
= 4398

Percentage of the number of letters that Copier Z printed over the total number of letters printed
= ⁴³⁹⁸₆₉₁₈ x 100%
≈ 63.57%

Answer(s): 63.57%