5 printers can print 5 sheets in 5 seconds. If I need to print 20 sheets in 20…

This is a rate-scaling problem: when the required output and the available time both increase by the exact same multiplying factor from a known baseline, the number of machines needed to meet the new target stays the same as the baseline — because the ratio of output to time (the rate that determines machine count) is unchanged.

1. Baseline: 5 printers together produce 5 sheets in 5 seconds, so each printer's own rate is 1 sheet every 5 seconds (5 printers producing 5 sheets in that same 5-second window means each contributes one sheet).

2. New target: 20 sheets in 20 seconds is exactly 4 times the baseline sheets (5 × 4 = 20) and exactly 4 times the baseline time (5 × 4 = 20) — quantity and time have scaled by the identical factor of 4.

3. Because a single printer's output over 20 seconds is also 4 times its baseline output (1 sheet × 4 = 4 sheets), the number of printers required is 20 sheets ÷ 4 sheets per printer = 5 printers — the same count as the baseline.

4. The office already has 5 printers, so the number of additional printers to install is 5 − 5 = 0.

Cross-check: with the existing 5 printers, each produces 4 sheets in the 20-second window, giving a total of 5 × 4 = 20 sheets — exactly the target — confirming that no extra printers are required.