years are usually about 365 days on earth (typo? wrong planet?)
daily rate r = 0.10/365 = 0.0002740
every day multiply by (1+r)
so after n days you have
w (1+r)^n
from july 25 to aug 13, n = 31-25 + 13 = 19
so on aug 13 dawn you have w (1+r)^19 and
at midnight you have [ w (1+r)^19 - 600 ]
now you figure out m days from aug 13 to dec 31
and we have on dec 31
[ w (1+r)^19 - 600 ](1+r)^m = 8900
[w (1.000240)^19 ] (1.000240)^m = 8900
solve for w
2. A sum of money, X was deposited in a savings account at 10% compounded daily on 25 July 1993. On 13 August 1993, RM600 was withdrawn and the balance as on 31 December 1993 was RM8900. Calculate the value of X using exact time and 360 day year
2 answers
Dear Damon, there nothing wrong with assuming a year has 360 days. It's called the "Banker's Rule".
This is the way how we can calculate it.
RM8,900 = [ X (1+0.1/360)^19 - RM600](1+0.1/360)^140
RM8,900/(1+0.1/360)^140 = X (1+0.1/360)^19 - RM600
RM8560.58 + RM600 = X (1+0.1/360)^19
RM9160.58 = X (1+0.1/360)^19
RM9160.58/(1+0.1/360)^19 = X
RM9112.36 = X
Therefore, X is RM9112.36#
This is the way how we can calculate it.
RM8,900 = [ X (1+0.1/360)^19 - RM600](1+0.1/360)^140
RM8,900/(1+0.1/360)^140 = X (1+0.1/360)^19 - RM600
RM8560.58 + RM600 = X (1+0.1/360)^19
RM9160.58 = X (1+0.1/360)^19
RM9160.58/(1+0.1/360)^19 = X
RM9112.36 = X
Therefore, X is RM9112.36#