By seeling both trouser, he has neither gain nor loss as on one trouser he had gain of ₹90 but on another one he has loss of ₹90. So he gained same amount and lost same amount which resulted in that he has neither gain nor loss.

Solution:

To find the total loss or gain, we need to calculate the individual gain or loss on each trouser and then add them up.

Given:
Price of each trouser sold = Rs. 900

Calculating Gain or Loss on the First Trouser:
- The seller gained 10% on the first trouser.
- The gain percentage can be calculated using the formula:
Gain Percentage = (Gain / Cost Price) * 100
- Since the gain percentage is given as 10%, we can calculate the gain on the first trouser as:
Gain = (10/100) * Cost Price
= (10/100) * 900
= 90

Calculating Gain or Loss on the Second Trouser:
- The seller lost 10% on the second trouser.
- The loss percentage can be calculated using the formula:
Loss Percentage = (Loss / Cost Price) * 100
- Since the loss percentage is given as 10%, we can calculate the loss on the second trouser as:
Loss = (10/100) * Cost Price
= (10/100) * 900
= 90

Calculating Total Loss or Gain:
To find the total loss or gain, we need to add the gains and losses on both trousers.

- Gain on the first trouser = 90
- Loss on the second trouser = 90

Total Gain or Loss = Gain on first trouser + Loss on second trouser
= 90 + (-90) (since loss is considered negative)
= 0

Conclusion:
The seller did not have any total loss or gain. The gain on the first trouser was offset by the loss on the second trouser. Therefore, the total loss or gain is 0.