By selling two tables for 1200 each, a man gains 10% on one and loses 10% on the other. What is his gain/loss percent in the whole transaction?
I calculated cost price for table one by equating selling price to 1.1 cost price.and got the cost price as 1,091(approx) and for table 2 I equated selling price to .9 cost price which comes out to be 1,333 (approx). Total cost price becomes 2024. There is a loss of 24. Now if I calculate loss on cost price the answer is 0.99 which is close to the answer given in the book which 1% loss.
Is there some other easier way to solve this?
As said before, there is no easier way to solve this. However, you can avoid any rounding errors by calculating at the very last step, instead of using approximations.
Calculate $\frac{1200}{1.1} + \frac{1200}{0.9}$ directly, as to get the original price, you undo the $1.1$ and $0.9$ multipliers on the tables.
Then the percentage change is:
$$\frac{\text{new} - \text{old}}{\text{old}} = \frac{2400-(1200/1.1 + 1200/0.9 )}{1200/1.1 + 1200/0.9} \times 100 \% \approx -1.01 \%$$
or approximately a $1 \%$ decrease.