Person A borrows Rs. 4000 from another person B for a duration of 4 years. He borrows a portion of it at 3% simple interest per annum, while the rest at 4% simple interest per annum. If B gets Rs.…

The amount borrowed at 3% was Rs. 3,000. At 4% for four years the full Rs. 4,000 would incur Rs. 640, and using the lower rate saves $4(0.04-0.03)=0.04$ rupees per rupee borrowed. The Rs. 120 difference therefore gives $120/0.04=3000$, while Rs. 1,000 is the amount borrowed at 4%.