Length will be the radius, so r = 21cm
Minute hand covers 360o in 60 minutes
So in 30 minutes it covers = 180 degree
Area of arc = angle it makes/360 * πr^2
So area covered = 180/360 * 22/7 * 21 * 21 = 693cm^2
The wonder is not that mathematics describes the world so well but that it describes it at all.
Unknown
The difference between a two-digit number and the number obtained by interchanging the digits is 36. What is the difference between the sum and the difference of the digits of the number if the ratio between the digits of the number is 1 : 2 ?