Step 1: Let the total cost of the projector be C. The amount paid at the time of purchase is 20% of C, which is ₹6,000. So,
\[ \frac{20}{100} C = 6000 \Rightarrow C = \frac{6000 \times 100}{20} \]
Step 2: The remaining amount is:
\[ 100\% - 20\% = 80\% \text{ of } C. \]
Amount payable at installation:
\[ \frac{80}{100} \times 30,000 = 24,000. \]
Conclusion: The amount payable at the time of installation is ₹24,000.
In a survey, 60 % of 200 students prefer online classes, and 25 % of the remaining prefer hybrid classes. How many students prefer neither?