How many bricks are used to construct the wall ?

Question

The outer dimensions of a cubical room are 8m*6m*4m (roof is not included in the dimension).
If the size of brick used (including cement) are 20cm*10cm*8cm.
Then how many bricks are used to construct the wall ?

Answer 1

6900 bricks
Logic : Dimension of cubical room is 800*600*400 (Converted to cm)
Size of brick used : 20*10*8

So, first side we can use (800/20)*(400/8) bricks. that is, 2000 bricks.
The opposite side of this wall we can use the same, that is 2000 bricks.
hence the other to sides length is now decremented by 20. that is 580.
these side we can use {(580/20)*(400/8)}*2 bricks. that is 2900 bricks.

Then the total number of bricks used = 6900 .