There are 648 cows and sheep on the farm. The ratio of the number of Cows to the number if sheep is 5:4. At an auction 2 thirds of the sheep and some cows are sold. The ratio of the number of cows to the number if sheep left is now 3:1. How many cows are sold?

Cows : sheep = 5 : 4

5x + 4x = 648

9x = 648

x = 72

5x = 5 * 72 = 360

4x = 4 * 72 = 288

There are originally 360 cows and 288 sheep.

2/3 of the sheep are sold. That means that 1/3 of the sheep are left.

1/3 * 288 = 96

96 sheep are left.

x cows were sold.

(360 - x) / 96 = 3/1

360 - x = 288

-x = - 72

x = 72

72 cows were sold