In a shopping centre that sells skirts, 3520 yellow skirts were sold and 10% of the remaining skirts that were sold were black. Of the leftover, 50% of the skirts sold were purple skirts and the rest were blue skirts. Given that the number of blue skirts sold was 5% of the total number of skirts sold, how many black and yellow skirts were sold altogether?
10% = ¹⁰₁₀₀ = ¹₁₀
50% = ⁵⁰₁₀₀ = ¹₂
5% = ⁵₁₀₀ = ¹₂₀

Yellow	Black	Purple	Blue
3520	1x2	9x2
		1x9	1x9
19x9			1x9
160 u	2 u	9 u	9 u

The total number of purple and blue shirts is the combined repeated identity. Make the total number of purple and blue shirts the same. LCM of 9 and 2 is 18.

The number of blue shirts is repeated. Make the number of blue shirts the same. LCM of 9 and 1 is 9.

Number of yellow skirts
= 171 u - 2 u - 9 u
= 160 u

160 u = 3520

1 u = 3520 ÷ 160 = 22

Number of black and yellow skirts
= 2 u + 3520
= (2 x 22) + 3520
= 44 + 3520
= 3564

Answer(s): 3564