If compound interest for 13th year is Rs. 1715 at 16(2 )/3 % p.a. The…

16\(\frac{2 }{3}\)% = \(\frac{1}{6}\) ⇒ \(\frac{7 → Amt.}{6 → Pri.}\)

For three years gap:

              10th year : 13th year

C.I.      :       6³       :       7³

                    216      :     343

Here,

343R = 1715

1R = 5

216R = 216 × 5 = 1080 = Sum at 10th year.