Tank X contained 4 times as many guppies as Tank Y. When 50% of the guppies in Tank X and 10% of the guppies in Tank Y were transferred to Tank Z, Tank Z had 210 guppies, which was 25% more guppies than before. How many less guppies were there in Tank Y than Tank X in the end?

	Tank X	Tank Y	Tank Z
Before	4 u	1 u	4x2.1 = 8.4 u
Change	- 2 u	- 0.1 u	+ 1x2.1 = + 2.1 u
After	2 u	0.9 u	5x2.1 = 10.5 u

Number of guppies that were transferred from Tank X to Tank Z
= 50% x 4 u
= ⁵⁰₁₀₀ x 4 u
= 2 u

Number of guppies that were transferred from Tank Y to Tank Z
= 10% x 1 u
= ¹⁰₁₀₀ x 1 u
= 0.1 u

25% = ²⁵₁₀₀ = ¹₄

Some guppies from Tank X and Tank Y were transferred to Tank Z.  The total number of guppies transferred from Tank X and Tank Y into Tank Z is the same.

Total number of guppies transferred from Tank X and Tank Y into Tank Z
= 2 u + 0.1 u
= 2.1 u

10.5 u = 210

1 u = 210 ÷ 10.5 = 20

Number of less guppies in Tank Y than Tank X
= 2 u - 0.9 u
= 1.1 u
= 1.1 x 20
= 22

Answer(s): 22