The length of the diagonal of a rhombus is 80% of the length of the other diagonal, Then the area of the rhombus is how many times the square of the length of the longer diagonal?

Let length of the longer diagonal = d cm
Then, length of other diagonal = 0.8 x d cm
Area of rhombus = (1/2) x d x 0.8 x d = 2/5 d²
= 2/5 d²
Area of square of the length of the longer diagonal = d²
So the area of the rhombus is 2/5 times the square of the length of the longer diagonal.