Answer: 39 cm
SOLUTION
Given,
Length, L = 30 cm
Breadth, B = 15 cm
Height, H = 20 cm.
The longest length of a 1 cm diameter wooden dowel that could fit inside the box = The diagonal, D of the box (from the lower front left corner to the upper back right corner)
Diagonal, D = ?
D^2 = L^2 + B^2 + C^2
D^2 = 30^2 + 15^2 + 20^2
D^2 = 900 + 225 + 400
D^2 = 1525
D = 39 cm (to the nearest whole centimeter)
Therefore, the longest length of a 1 cm diameter wooden dowel that could fit inside the box is 39 cm (to the nearest whole centimeter).