The average number of pages Lucy read in a certain number of days was 12. In the next five days, Lucy read another 81 pages. As a result, the average number of pages she read increased to 15. How many days did Lucy read in total?
|
At first |
In the end |
Number |
1 u |
1 u + 5 |
Value |
12 |
15 |
Number x value |
12 u |
15 u + 75 |
Number of days that Lucy read at first = 1 u
Number of pages that Lucy read at first
= 1 u x 12
= 12 u
Number of pages that Lucy read in the end = 12 u + 81
Number of days that Lucy read in the end = 1 u + 5
Number of pages that Lucy read in the end
= 15 x (1 u + 5)
= 15 u + 75
15 u + 75 = 12 u + 81
15 u - 12 u = 81 - 75
3 u = 6
1 u = 6 ÷ 3 = 2
Number of days that Lucy read in the end
= 1 u + 5
= 2 + 5
= 7
Answer(s): 7