Pls help. Tks

When a pebble is dropped into a pool of water, circular ripples are formed. 2 consecutive ripples have a radius of 7 cm & 14 cm respectively. What is the percentage increase in the area of the ripples?

Pls help. Tks

When a pebble is dropped into a pool of water, circular ripples are formed. 2 consecutive ripples have a radius of 7 cm & 14 cm respectively. What is the percentage increase in the area of the ripples?

SAHMom

%increase

= increase / original X 100%

= (pi . R . R – pi . r . r) / (pi . r . r) X 100%

= (14 x 14 – 7 x 7)/(7 x 7) X 100% ( cancel out pi)

= (7 x 7) (2 x 2 -1 x 1)/(7 x 7) X 100% (if in paper 1 without calculator)

= 300%#

Alternatively, if kids know higher level concepts (not necessary at P6)

Ratio of sides = 2:1

Ratio of areas = 2^2: 1^2 = 4:1

Area increase is 3 parts, from 1 part to 4 parts

% increase = 300%#

gnihs

Thanks and appreciate SAHmom.

Bec I wondering which pi value to use. After seeing ur wking, realise that pi automatically being cancel off.