The ratio of the number of wafers in Container C to the number of wafers in Container D was 7 : 5. 40% of the wafers in Container C and 0.8 of those in Container D were mocha. After transferring the wafers between the 2 containers, the number of mango wafers in both containers are the same. Likewise, the number of mocha wafers in both containers are the same. If a total of 220 wafers were moved, how many more wafers were there in Container C than Container D at first?

Container C		Container D
7 u		5 u
Mocha	Mango	Mocha	Mango
2.8 u	4.2 u	4 u	1 u
+ 0.6 u	- 1.6 u	- 0.6 u	+ 1.6 u
3.4 u	2.6 u	3.4 u	2.6 u

Number of mocha wafers in Container C
= 40% x 7 u
= ⁴⁰₁₀₀ x 7 u
= 2.8 u

Number of mango wafers in Container C
= 7 u - 2.8 u
= 4.2 u

Number of mocha wafers in Container D
= 0.8 x 5 u
= 4 u

Number of mango wafers in Container D
= 5 u - 4 u
= 1 u

Number of mocha wafers in each container in the end
= (2.8 u + 4 u) ÷ 2
= 6.8 u ÷ 2
= 3.4 u

Number of mango wafers in each container in the end
= (4.2 u + 1 u) ÷ 2
= 5.2 u ÷ 2
= 2.6 u

Number of wafers moved
= 0.6 u + 1.6 u
= 2.2 u

2.2 u = 220

1 u = 220 ÷ 2.2 = 100

Number of more wafers in Container C than Container D at first
= 7 u - 5 u
= 2 u
= 2 x 100
= 200

Answer(s): 200