Rita uses 10 buttons on each rag doll she makes for her toy business. Two-fifths of the buttons she uses are blue and the rest are red. If Rita makes 115 rag dolls, how many red buttons does she use?

Number of rag dolls made by Rita = 115

Number of buttons Rita uses on each rag doll = 10

Then

Total number of buttons required by Rita = 115 * 10

= 1150

Number of blue buttons used by Rita = (2/5) * 1150

= 2 * 230

= 460

Then

The total number of red buttons used by Rita = 1150 - 460

= 690

So Rita uses 690 red buttons for making 115 rag dolls. I hope the procedure is clear enough for you to understand.