In a pack of construction paper, the numbers of blue and red sheets are originally in the ratio 2:7. Each day, Laura uses 1 blue sheet and 3 red sheets. One day, she uses 3 red sheets and the last blue sheet, leaving her with 15 red sheets. How many sheets of construction paper were in the pack originally?
B/R = 2/7
Last day she had =15 + 3 =18 red + 1 blue =19 sheets
Since she has 15 red left from a ratio of B/R=2/7,that means she must have started with:
15 x 7 = 105 red sheets and 2/7 x 105 = 30 blue sheets =135 sheets in the original pack of paper.
135 - 19 =116 sheets that were used over a period of 4 sheets per day: 116/4 =29 days.
105 - 29*3 =18 red sheets left for last day
30 - 29*1 = 1 blue sheet left for last day.
