The average number of pages Irene read in a certain number of days was 13. In the next three days, Irene read another 87 pages. As a result, the average number of pages she read increased to 15. How many days did Irene read in total?
|
At first |
In the end |
Number |
1 u |
1 u + 3 |
Value |
13 |
15 |
Number x value |
13 u |
15 u + 45 |
Number of days that Irene read at first = 1 u
Number of pages that Irene read at first
= 1 u x 13
= 13 u
Number of pages that Irene read in the end = 13 u + 87
Number of days that Irene read in the end = 1 u + 3
Number of pages that Irene read in the end
= 15 x (1 u + 3)
= 15 u + 45
15 u + 45 = 13 u + 87
15 u - 13 u = 87 - 45
2 u = 42
1 u = 42 ÷ 2 = 21
Number of days that Irene read in the end
= 1 u + 3
= 21 + 3
= 24
Answer(s): 24