Sarah and Yoko collected buttons. Yoko gave 70% of her buttons to Sarah. As a result, Sarah's buttons increased by 30%. If Sarah had 819 buttons left, find the total number of buttons the two girls had at first.
| |
Comparing the change
in Yoko's buttons |
Yoko |
Sarah |
| Before |
10x3 =
30 u |
|
10x7 =
70 u |
| Change |
- 7x3 =
- 21 u |
- 3x7 =
- 21 u |
+ 3x7 =
+ 21 u |
| After |
3x3 =
9 u |
|
13x7 =
91 u |
70% =
70100 =
710 30% =
30100 =
310 The number of buttons that Sarah gave to Yoko is repeated. Make the number of buttons that Sarah gave to Yoko the same. LCM of 3 and 7 is 21.
Number of buttons that Sarah had in the end = 91 u
91 u = 819
1 u = 819 ÷ 91 = 9
Number of buttons that Yoko and Sarah had at first
= 30 u + 70 u
= 100 u
= 100 x 9
= 900
Answer(s): 900
