Mrs Lim had a total of 99 yellow and pink tulips in the ratio of 7 : 4. After she had given away 3 times as many yellow tulips as pink tulips, the number of yellow and pink tulips left was in the ratio of 4 : 3. How many more yellow tulips than pink tulips did she give away?

	Yellow	Pink	Total
Before	7 b	4 b	11 b
Change	- 3 u	- 1 u
After	4 p	3 p

	Make p the same (1)x3 = (3)	Yellow (1)	Pink (2)	Make p the same (2)x4 = (4)
Before	189	63	36	144
Change	- 9 u	- 3 u	- 1 u	- 4 u
After	12 p	4 p	3 p	12 p

Number of tulips at first
= 7 b + 4 b
= 11 b

11 b = 99

1 b = 99 ÷ 11 = 9

Number of yellow tulips at first
= 7 b
= 7 x 9
= 63

Number of pink tulips at first
= 4 b
= 4 x 9
= 36

63 - 3 u = 4 p --- (1)

36 - 1 u = 3 p --- (2)

Make p the same.

(1)_x3 
189 - 9 u = 12 p --- (3)

(2)_x4 = (4)
144 - 4 u = 12 p --- (4)

(3) = (4)
189 - 9 u = 144 - 4 u
9 u - 4 u = 189 - 144
5 u = 45

1 u = 45 ÷ 5 = 9

Number of more yellow tulips than pink tulips that she gave away
= 3 u - 1 u
= 2 u
= 2 x 9
= 18

Answer(s): 18