**Cost of Thousand Bricks**

The given information states that the cost of a thousand bricks is 1800 rupees. This means that for every 1000 bricks, the cost is 1800 rupees.

To find the cost of 30000 bricks, we can use the concept of proportion.

**Proportion**

A proportion is a statement that two ratios are equal. In this case, we can set up a proportion to find the cost of 30000 bricks.

Let's set up the proportion as follows:

(Number of bricks) / (Cost of bricks) = (Total number of bricks) / (Total cost of bricks)

We know:
(Number of bricks) = 1000
(Cost of bricks) = 1800

Substituting these values into the proportion:

1000 / 1800 = 30000 / (Total cost of bricks)

**Cross-Multiplication**

Cross-multiplication is a method used to solve proportions. It involves multiplying the numerator of one ratio by the denominator of the other ratio and setting the two products equal to each other.

Using cross-multiplication, we can solve for the total cost of bricks:

1000 * (Total cost of bricks) = 1800 * 30000

**Calculation**

Let's calculate the total cost of 30000 bricks using the equation above:

1000 * (Total cost of bricks) = 1800 * 30000

Total cost of bricks = (1800 * 30000) / 1000

Total cost of bricks = 54000000 / 1000

Total cost of bricks = 54000 rupees

**Answer**

Therefore, the cost of 30000 bricks is 54000 rupees.

Cost of 1000 bricks = 1800 ,so cost of 30,000 bricks = 1800× 30 = 54000
therfore the answer is Rs 54,000