Since ∠B = 90°
Using pythagoras theorem
AC2 = AB2 + BC2 = 202 + 152
= 400 + 225
AC2 = 625
AC2 = 255
AC = 25
Area of a triangle ΔABC = 1/2 × 15 × 20 = 150 feet2
Again Area of ΔABC = 1/2 × AC × BD
150 = 1/2 × 25 × BD
BD = (2×150)/25 = 300/25
BD = 12 feet
∴ Length of the altitude on the hypotenuse of the right angled triangle is 12 feet.