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PoetVogon
Original investment be 90
Five-ninths = 50 and remaining i.e four-ninths = 40

Investment 01: 50(1+2r/2)^(2*1) = 50(1+r)^2 ...(1)
Investment 02: 40(1+r) ... (2)

Investment 1+2 = 4/3 of 90
50(1+r^2+2r) + 40 +40r = 120
50r^2 + 140r - 30 = 0
5r^2+14r + 3 = 0
(r+3) (5r-1) = 0
Therefore, r=1/5 or 20%

Answer: C
Hi, I like your explanation but I can't follow your last step:

5r^2+14r + 3 = 0 [it should be -3 here but thats probably just a typo
(r+3) (5r-1) = 0

I solved it via the pq-method but that obviously takes a bit time. So can you please elaborate on your method?



he has split the 14r in such a manner that the r^2 term and the constant at last both get a common.

you do this by taking the lcm of the square term and the constant and split in such a fashion that it gives common to both.

LCM of 5 and 3 is 15,
now
split 15 to get a 14, in terms of common terms of 5 and 3 respectively.

eg
5r^2 +15r-r-3=0
now
5r(r+3)-1(r+3)=0
(5r-1) (r+3)=0
so , r=1/5 or -3

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