7. See the numbers for yourselves
1 floor consumes 5 rs electricity every hour
For 6 hrs(one night), we save 30rs per floor.
1 hostel=3floors. 1 hostel saves 30 x 3 =90rs
per night.
Total no of hostels= 19+5=24. Money saved
per night= 24 x 90 =2,160rs.
So in a year we save 2,160 x 365= 7,88,400rs.
Sensor cost =1000rs per floor
Cost for all hostels= 24 x 3 x 1000= 72000rs.