ARITHMETIC FORMULAE ON SIMPLE INTEREST
= 100P/[100T + rT(T – 1)/2]18). If A1 is the amount of principle P at time period t with r1% interest rate , and A2 is the amount of principle if rate of simple interest is r2% , then principle P is = (A2r1 – A1r2)/(r1 – r2) and time period t is = (A2 – A1)100/(A2r1 – A1r2)
19). A1 is the amount of principle P in time period t1 with any interest rate r% , and A2 is the amount of principle if time period is t2 , then principle P is = (A2t1 – A1t2)/(t1 – t2) and interest rate is
= (A2 – A1)100/(A2t1 – A1t2)
20). SI1 is the simple interest of a principle P1 in t1 years with r1% interest rate. And SI2 is the simple interest of a principle P2 in t2 years with r2% interest rate , then difference in simple interest is
SI2 – SI1 = (P2r2t2 – P1r1t1)/100
If only time changes and all parameters are constant then-
*. SI2 – SI1 = Pr(t2 – t1)/100
*. If only rates changes then-
SI2 – SI1 = Pt(r2 – r1)/100
*. If only principle changes then –
SI2 – SI1 = rt(P2 – P1)/100
IF TWO PARAMETERS CHANGES
*. Only change in rate and time then-
SI2 – SI1 = P(r2t2 – r1t1)/100
*. Only change in principle and time
SI2 – SI1 = r(P2t2 – P1t1)/100
*. Only change in principle and rate
SI2 – SI1 = t(P2r2 – P1r1)/100
21). If 1/x part of a principle P is lent out at r1% rate, 1/y part is at r2% rate and remaining 1/z part is at r3% interest rate , and in this way simple interest received is SI , then
Principle P is = SI × 100/(r1/x +r2/y + r3/z)
22). The rate on which simple interest become n times of principle in t years is = 100n/t
23). Simple interest if amount is given –
SI = A × r × t/(100 + rt)
24). If a principle P is given to the bank in n equal installments at r% rate per annum , then amount of each installment is = P(1+ nr/100)
25) Mind it
*. If rate of interest is half yearly then rate and time is = r/2% and 2t
*. If rate of interest is quarterly then rate and time is = r/4% and 4t
*. If rate of interest is monthly then rate and time is = r/12% and 12t.