ANSWER:
6_34/99
STEP:
So yes. When a decimal is repeating, you can take the repeating number (most likely a decimal) and put 99 under it. Since 99 cannot be solved, you put 99. So, 34/99. Though we are not finished. There is still the whole 6 number left. So, you do 6_34/99.
Proof:
10x=6.6...
-x=-0.6...
9x=6
x=6/9=1/3.
The profit is 5rs because 25-20=5rs
(a-b) X (a+b)
= aXa - bXa +aXb -bXb (distributing)
Now, cross product of a vector with itself = 0
so, aXa = 0, bXb = 0
Also, aXb = - bXa
so,
(a-b) X (a+b) = 0 + aXb + aXb + 0
= 2aXb
hence, proved :)