Ashop recorded total sales of $2,000 on monday. on tuesday, its sales fell by 10%. on wednesday, sales fell by another 20% compared with tuesday. from wednesday to thursday, sales increased by an amount equal to 25% of monday’s total sales. what is the net change in total sales from monday to thursday?

The shop had $2,000 in sales on Monday. 
If it fell by 10% on Tuesday, then 2000 * 0.10 equals the percentage it dropped, so it dropped by $200. So they only had $1,800 in sales on Tues. 
If they fell by another 20% on Wednesday, 1,800 * 0.20 equals a $360 drop. Now we're at $1,440. 
The sales then increased by 25% of Monday's total # of sales. 25% of Monday's sales is 2,000 * 0.25 which equals a $500 increase. Now we're at $1,940. 
Now that we're done with everything, how far are we from the beginning? That's the net change. :) We began at $2,000 on Monday, and ended with $1,940 on Thursday. 2000 - 1940 is 60, so 60 = your net change. 

TLDR: Sold $2,000 on Mon, sold $1,800 on Tues, sold $1,440 on Wed, and then sold $1,940 on Thurs. The net change is $60.