Abi has a bag containing some blue and red pens. If she adds in 11 blue pens, 20% of the pens in the bag are red. If she adds in another 24 red pens, 50% of the pens in the bag are red. How many blue pens are in the bag?
| |
Blue pens |
Red pens |
| Before |
4 u - 11 |
1 u |
| Change 1 |
+ 11 |
|
| After 1 |
4x1 =
4 u |
1x1 =
1 u |
| Change 2 |
|
+ 24 |
| After 2 |
1x4 =
4 u |
1x4 =
4 u |
20% =
20100 =
1550% =
50100 =
12The number of blue pens remains unchanged at the second change when she adds in another 24 red pens. Make the number of blue pens the same at the second change. LCM of 4 and 1 is 4.
Number of red pens added
= 4 u - 1 u
= 3 u
3 u = 24
1 u = 24 ÷ 3 = 8
Number of blue pens at first
= 4 u - 11
= 4 x 8 - 11
= 32 - 11
= 21
Answer(s): 21
