security code conversion?

Question

Two friends Alich and Delich use the following code number system in their business for the purpose of security:

They use 10, 9, ..., 1 for 1, 2,....,10 respectively; 20, 19, ..., 11 for 11, 12, ..., 20 respectively; 30, 29,...2l for 21, 22,..., 30 respectively; and so on. Alich told Delich "I bought a rim of paper for Rs 12100 and sold the same for Rs 12095".... What was the actual loss or gain incurred by Alich ?

(1)Gain ,Rs 5
(2)Gain, Rs 4
(3)Loss, Rs 4
(4)Gain , Rs 13

here is the solution and my doubt
http://docs.google.com/Doc?id=dc83hzcs_205cgt77n

Answer 1

Their code has

10 means 1
20 means 11
30 means 21
40 means 31
etc.

so for any "coded" number that ends in zero, subtract 9 to "decode" it. Therefore, 12100 is code for 12100-9 = 12091

Do the same thing for numbers that end in 5:

5 means 6
15 means 16
25 means 26
etc.

so for any "coded" number ending in 5, add 1 to get the "decoded" number. So 12095 decodes to 12096.

So answer #1 is correct.