2 days ago, Jade had a total of 140 silver and black stamps. 25% of her stamps were black stamps. Today, her younger sister gave her some more stamps. As a result, her silver stamps increased by 20%. Now, 50% of her stamps are black stamps. How many black stamps did her younger sister give her?
| |
Black stamps |
Silver stamps |
Total
stamps |
| Before |
1 u |
3 u |
140 |
| Change |
+ 2.6 u |
+ 0.6 u |
|
| After |
3.6 u |
3.6 u |
|
Comparing the
silver stamps and
black stamps in the end |
1 |
1 |
|
25% =
25100 =
14 Black stamps : Silver stamps = 1 : 3
Increase in the number of silver stamps
= 20% x 3 u
=
20100 x 3 u
= 0.6 u
50% =
50100 =
12 In the end
Black stamps : Silver stamps = 1 : 1
Number of stamps at first
= 3 u + 1 u
= 4 u
4 u = 140
1 u = 140 ÷ 4 = 35
Number of black stamps that Jade received from her younger sister
= 3.6 u - 1 u
= 2.6 u
= 2.6 x 35
= 91
Answer(s): 91
