Given:

First man can build the wall in 9 hours
Second man can build the wall in 10 hours

Let total number of bricks in the wall = x

Step 1: Find individual work rates (bricks per hour)

First man’s rate = x / 9
Second man’s rate = x / 10

Working together (normal rate):
= x/9 + x/10
= (10x + 9x) / 90
= 19x / 90 bricks per hour

Step 2: Given condition while working together

They use 100 bricks less per hour
And complete the wall in 5 hours

So, their **actual working rate** =
= (Total bricks) / 5
= x / 5

But this rate is 100 bricks less than normal combined rate:

19x/90 − 100 = x/5

Step 3: Solve the equation

Multiply both sides by 90:

19x − 9000 = 18x

⇒ 19x − 18x = 9000

⇒ x = 9000

Final Answer:

Total number of bricks in the wall = **9000 bricks**