To find how many days Ravi remained absent, we need to calculate 85% of the total 220 working days to determine how many days he attended and then subtract that from the total days.

1. Step 1: Calculate the number of days Ravi attended. $85\% \text{ of } 220 = \frac{85}{100} \times 220 = 187 \text{ days}$

2. Step 2: Subtract the days attended from the total days to find the days he was absent. $220 - 187 = 33 \text{ days}$

Therefore, Ravi remained absent for 33 days.

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Here are five related questions to expand on this concept:

1. If Ravi's attendance was 90%, how many days would he be absent?
2. How many days would Ravi have attended if the school had 250 working days and his attendance was still 85%?
3. What is the minimum attendance percentage required for Ravi to have attended at least 200 days?
4. If another student had 75% attendance, how many days were they absent in a 220-day school year?
5. How would the calculation change if the school had only 180 working days?

Tip: When working with percentages, multiplying the total amount by the percentage (in decimal form) gives the desired portion directly.