Min, Mary, Xylia and Abi jointly contributed to the cost of a present for their classmate. Min's contribution is ¹₅ of the total contribution made by the four girls. The ratio of Abi's contribution to the total of Mary's and Xylia's contribution is 3 : 1. What is the total contribution by the four girls if Mary's contribution is ¹₄ of Xylia's contribution and the total amount contributed by Min and Abi is $280?

Min	Mary	Xylia	Abi	Total
1x5	4x5			5x5
	1x5		3x5
	1x1	4x1
5 u	1 u	4 u	15 u	25 u

Working backwards.

Total amount that Mary and Xylia had is the combined repeated identity.
LCM of 1 and 5 = 5

Total amount that Mary, Xylia and Abi had is the next combined repeated identity.
LCM of 4 and 5 = 20 

Total amount contributed by Min and Abi
= 5 u + 15 u
= 20 u

20 u = 280

1 u = 280 ÷ 20 = $14

Total contribution by the four girls
= 25 u
= 25 x 14
= $350

Answer(s): $350