A room is 4 m × 3 m with 20 cm walls all around. The estimate of walls by central line method will be 

Explanation:

Center line method

In this method of estimation, the total centerline length of walls in a building is first calculated, then the center line length is multiplied with the breadth and depth of the respective items to get the total quantity at a time.

Deductions

L Junction - There is no need to deduct from total centreline length.

T Junction - Half (1/2) breadth wall measurement should be deducted for a T junction.

Calculation:

Estimate be central line method is as follows:

[(4+0.1+0.1)×2] + [(3+0.1+0.1)×2] = [8.4] + [6.4] = 14.8 m