Erika bought some stamps. She gave
15 of the stamps to her sister and sold
25 of the remaining stamps. After that, she bought another 39 stamps and had the same number of stamps that she bought at first. How many stamps did Erika buy at first?
| Her sister |
Remaining stamps |
Bought stamps |
Total |
1x5 =
5 u |
4x5 =
20 u |
|
5x5 =
25 u |
| |
Sold |
Left |
|
|
| |
2x4 |
3x4 |
|
|
| 5 u |
8 u |
12 u |
39 |
|
The remaining number of stamps before Erika bought another 39 stamps is repeated. Make the remaining number of stamps the same. LCM of 4 and 5 is 20.
Total number of stamps at first = 25 u
Number of stamps that Erika had left and bought after that = 12 u + 39
25 u = 12 u + 39
25 u - 12 u = 39
13 u = 39
1 u = 39 ÷ 13 = 3
Total number of stamps at first
= 25 u
= 25 x 3
= 75
Answer(s): 75
