Answer : 50 degree .
Properties to use : Diagonals are equal and they bisect each other .
Draw the figure to understand :
So in one of the small triangles triangles where you take 25 degree .
Then since diagonals are equal and they bisect , we would have an isoscseles triangle .
So its angles would be 25 , 25 , 130 .
Now the acute angle between the two diagonals = ( 180 - 130 ) = 50 .