The total weight of the packages is 5/8 = 0.625 + 2/3 = 0.666 i.e. 1.291 Pound.
TO be precise 2/3 would be 0.666666667, so technically the total weight of the two packages is 1.291666667 Pound.
To calculate the exact difference between Rosa's first and second package, we would have to subtract the weight of the second package with the weight of the first package: 0.666666667 - 0.625 = 0.041666667.
So, Rosa's second package is heavier by 0.041666667 pound.