A certain sum (in ₹)is invested at simple interest at y% per annum for at $3\frac{1}{2}$ years. Had it been invested at (y + 4) % per annum at simple interest, it would have fetched ₹4,452 more as interest. What is the sum?

₹31,800

Difference of Rate of 1 year = 4%

Difference of Rate of \(\frac{7}{2}\) years = 4%  × \(\frac{7}{2}\) = 14 %

⇒ 14% =  Rs 4452

⇒ 100%= Rs 4452 × \(\frac{100}{14}\) = Rs. 31800