Introduction
Ravi wants to buy a machine that costs Rs 9,05,000. He has Rs 6,43,578. In order to buy the machine, he needs to borrow some money. The question is how much he should borrow so that he is left with Rs 25,000 after buying the machine.

Calculation
To calculate how much Ravi should borrow, we need to subtract the cost of the machine and the amount he wants to be left with from his current balance. Therefore, the calculation would be as follows:

Amount Ravi needs to borrow = Cost of machine - (Current balance - Amount he wants to be left with)
Amount Ravi needs to borrow = Rs 9,05,000 - (Rs 6,43,578 - Rs 25,000)
Amount Ravi needs to borrow = Rs 9,05,000 - Rs 6,68,578
Amount Ravi needs to borrow = Rs 2,36,422

Therefore, Ravi needs to borrow Rs 2,36,422 in order to buy the machine and be left with Rs 25,000.

Explanation
Ravi wants to buy a machine that costs Rs 9,05,000. However, he only has Rs 6,43,578. Therefore, he needs to borrow some money in order to buy the machine. After buying the machine, he wants to be left with Rs 25,000.

To calculate how much he should borrow, we need to subtract the cost of the machine and the amount he wants to be left with from his current balance. The result of this calculation tells us how much he needs to borrow.

In this case, Ravi needs to borrow Rs 2,36,422 in order to buy the machine and be left with Rs 25,000. This means that he will have to pay back this amount along with any interest that may be charged by the lender. It is important to consider the interest rate and the repayment terms before borrowing any money.