Question

You purchased a phone by paying a down payment of
Rs.3000 and 6 monthly
installments of Rs.225 each.
How much did you pay for the phone in total?
a)Rs.3225
b)Rs.4350.
c)Rs.5375.
d)Rs.6550.

Answer 1

For example, if the total loan for 5 months, the seller gets 4 months interest on the 1st installment, 3 months interest on the 2nd installment, 2 months interest on the 3rd installment, 1 month interest on the 4th installment, no interest on 5th installment.
P+P×t×R100×12P+P×t×R100×12 = (x+x×(t−1)×R12×100)(x+x×(t−1)×R12×100)+ (x+x×(t−2)×R12×100)(x+x×(t−2)×R12×100) + . . . . . + (x+x×R×212×100)(x+x×R×212×100) + (x+x×R×112×100)(x+x×R×112×100) + xx
Note: The above formula is for monthly installments.  If installment is asked per year, then no need to divide those terms with 12 
General formula for installment calculation: x=P(1+n×r100)n+n(n−1)2×r100x=P(1+n×r100)n+n(n−1)2×r100
(Note:  If you calculating monthly installments, replace "n" by number of months, and "r" by "r/12"
After simplification of the above formula, you get x=P(100+nr)100n+n(n−1)r2x=P(100+nr)100n+n(n−1)r2

If Amount will be given ( ∵∵ Principal + interest) then the following formula can be used : 100A100n+n(n−1)r2100A100n+n(n−1)r2
I Hope it will help!
^_^

Answer 2

if only 1 6 monthy installment is paid then 3225