In order to determine the ratio of the perimeters for the given rectangles, first calcualte their perimeters. Use the following formula:
P = 2w + 2l
w: width
l: length
For the smaller rectangle you have:
w = 2cm
l = 4 cm
P = 2(2cm) + 2(4cm) = 4cm + 8cm = 12cm
For the bigger triangle you have:
w' = 4cm
l' = 8cm
P' = 2(4cm) + 2(8cm) = 8cm + 16cm = 24cm
Then, you have:
P/P' = 12cm/24cm = 1/2
Hence, the ratio is 1:2
