50 paise coin=0.50 rupee
25 paise coin=0.25 rupee
Let's one rupee coin=x
Now making equation,
[5*x]+[6x*(0.5)]+[7x*(0.25)]=780
5x+3x+1.75x=780
x=80
so,
1 rupee coins=5*80=400
50 paise coins=6*80=480
25 paise coins=7*80=560
Ans is no of coins of each kind are 400, 480, & 560