The average number of pages Penelope read in a certain number of days was 17. In the next three days, Penelope read another 99 pages. As a result, the average number of pages she read increased to 21. How many days did Penelope read in total?
| |
At first |
In the end |
| Number |
1 u |
1 u + 3 |
| Value |
17 |
21 |
| Number x value |
17 u |
21 u + 63 |
Number of days that Penelope read at first = 1 u
Number of pages that Penelope read at first
= 1 u x 17
= 17 u
Number of pages that Penelope read in the end = 17 u + 99
Number of days that Penelope read in the end = 1 u + 3
Number of pages that Penelope read in the end
= 21 x (1 u + 3)
= 21 u + 63
21 u + 63 = 17 u + 99
21 u - 17 u = 99 - 63
4 u = 36
1 u = 36 ÷ 4 = 9
Number of days that Penelope read in the end
= 1 u + 3
= 9 + 3
= 12
Answer(s): 12
