Memory leak
The other day I sold two books I bought a few years back. One of them gave me a 20% profit, while the other gave me a 20% loss. Together, however, the two books gave me a 5% profit.
I can’t seem to remember how much I sold each bok for, although I do remember that the total sale price was 1260 baht.
Problem source: Rudi Kessel, Mattenøtter.
November 13th, 2009 at 12:15 am
Say you bought the first for a and the second for b, and sold the first for c and the second for d. Then
c = 1.2 a = 6a/5
d = 0.8 b = 4b/5
(c+d) = 1.05 (a+b) = 21(a+b)/20 = 1260 baht
RTF c, d.
a+b = 20(c+d)/21
a = 5c/6
b = 5d/4
5c/6 + 5d/4 = 20(c+d)/21
c/6 + d/4 = 4(c+d)/21
14c + 21d = 16(c+d)
5d = 2c
so you sold the books for:
c = (5/7)*1260 baht = 900 baht
d = (2/7)*1260 baht = 360 baht
Check:
a = 750
b = 450
You bought the books for 750+450=1200 baht, so your profit was 60 baht, which is 5% of that.