Hi Melody,
thank you for the rules.
(1) 2,8,25,50,75,100 Magic number is 431
five Numbers:
$$\left(
\dfrac{75}{100}+50
\right)*8+25=431$$
(2) 4,6,25,50,75,100 Magic number is 821
five Numbers:
6*(100+50) - 75 - 4 = 821 ( your solution )
6*(100+25) + 75 - 4 = 821 ( your solution )

