Paying Rings At Hotel

What was the condition? 

You can pay 7 rings in 7 days in following sequence.

Day 1 : 

Give the only ring that is in first set. Paid 1 ring.

Day 2 : 

Take back ring given on Day 1 & give second set of rings having 2 rings. Paid 2 rings

Day 3 :

Give 1 ring back again. Total rings paid = 2 + 1 = 3


Day 4 : 

Take both sets of rings back & give third set of rings which has 4 rings. So paid 4 rings.

Day 5 :

Next give first set of ring having only 1 ring. Paid 4 +1 = 5 rings.

Day 6 :

Take back 1 ring & give second set which has 2 rings. Paid 4 + 2 = 6 rings.

Day 7 :

Finally, again give back the first set having only ring. Paid 6 + 1 = 7 rings.

Hotel