In 2006, if sales value of B increases by 10% and that of A decreases by 10%. What is the percentage change in sales, if sale of all other brands remain same?

Let the total sales in 2005 be 100x, then we can calculate the shares of each of the 5 computer brands A, B, C, D and E as follows:

Now, in 2006, sales of B went up by 10%, so sales of B in 2006 = 1.1 times sales of B in 2005 = $$1.1\times\ 15x=16.5x$$

And, sales of A decreased by 10% , So sales of E in 2006 = 0.9 times sales of A in 2005 = $$0.9\times\ 45x=20.5x$$

The sales of C, D and E remain unchanged, hence we update the table by adding another column for 2006 and filling in the values as:

So the sales in 2006 decreased compared to 2005 .

The change can be expressed as percentage as $$\frac{Sales_{2006}-Sales_{2005}}{Sales_{2005}}\times\ 100\%=\frac{97x-100x}{100x}\times\ 100\%=-3\%$$

Hence, there was a 3% decrease in sales.