Question

It has to pay rs. 225/- as bill when 9 bulbs are used for 30 days using them for 4 hours per day. find the number of days if 5 bulbs are used for 6 hours per day for the payment of rs. 375/- against the bill.

Answer 1

According to question

for 9 Bulbs

Number of days   D1 = 30
time in each day   T1 = 4 Hrs
So time in  30 days  = 30 * 4 = 120 Hrs

So According to question
 
Bill for 120 hours * 9 = 225
For 1 Bulb
   Bill for 120 hrs for 1 bulb = 225 / 9 = 25 Rs

Thus cost of using one bulb for 1 hr = 25 /120

So
  T2 * 5 = 375
 D2 * 6 * 5 = 375
  D2 = 75/6