The average number of pages Gabby read in a certain number of days was 15. In the next three days, Gabby read another 87 pages. As a result, the average number of pages she read increased to 21. How many days did Gabby read in total?
| |
At first |
In the end |
| Number |
1 u |
1 u + 3 |
| Value |
15 |
21 |
| Number x value |
15 u |
21 u + 63 |
Number of days that Gabby read at first = 1 u
Number of pages that Gabby read at first
= 1 u x 15
= 15 u
Number of pages that Gabby read in the end = 15 u + 87
Number of days that Gabby read in the end = 1 u + 3
Number of pages that Gabby read in the end
= 21 x (1 u + 3)
= 21 u + 63
21 u + 63 = 15 u + 87
21 u - 15 u = 87 - 63
6 u = 24
1 u = 24 ÷ 6 = 4
Number of days that Gabby read in the end
= 1 u + 3
= 4 + 3
= 7
Answer(s): 7
