The rule for arriving at the capital dealt out at two different rates of interest:-
54.[54] Let the balance quantity (i.e., the difference between the two amounts of interest,) be divided by the difference between those (two quantities) which form the interest on one for the given periods of time; (this quotient) becomes the capital thought of by one's self before.
Examples in illustration thereof.
55. Borrowing at the rate of 6 percent, and then lending out at the rate of 9 per cent, one obtains in the way of the differential gain 81 duly at the end of 3 months. What is the capital (utilized here) ?
56. Borrowed at the rate of 3 per cent per mensem, a certain capital amount is put out to interest at the rate of 8 per cent per mensem. The differential gain is 80 at the end of 2 months. How much is the capital (so used)?
The rule for arriving at the time when both capital and interest will become paid up (by installments):-
57.[57] The capital lent out is multiplied by its time (of installment) and is again multiplied by the rate-interest; this product, when divided by the rate-capital and the rate-time, becomes the interest in relation to the installment. The capital (in the installment) and the time (of discharge of the debt are to be made out) as before from (this) interest.
Examples in illustration thereof.
58. The rate of interest is 5 for 70 per mensem; the (amount of the) installment to be paid is 18 in (every) 2 months; the capital lent out is 84. What is the time of discharge?
54.^ Symbolically, .
57.^ Symbolically, interest in the installment, where p is the time of each installment.
