The average number of pages Barbara read in a certain number of days was 13. In the next four days, Barbara read another 70 pages. As a result, the average number of pages she read increased to 15. How many days did Barbara read in total?
| |
At first |
In the end |
| Number |
1 u |
1 u + 4 |
| Value |
13 |
15 |
| Number x value |
13 u |
15 u + 60 |
Number of days that Barbara read at first = 1 u
Number of pages that Barbara read at first
= 1 u x 13
= 13 u
Number of pages that Barbara read in the end = 13 u + 70
Number of days that Barbara read in the end = 1 u + 4
Number of pages that Barbara read in the end
= 15 x (1 u + 4)
= 15 u + 60
15 u + 60 = 13 u + 70
15 u - 13 u = 70 - 60
2 u = 10
1 u = 10 ÷ 2 = 5
Number of days that Barbara read in the end
= 1 u + 4
= 5 + 4
= 9
Answer(s): 9
