Doubts regarding ratio topic in quantitative analysis

Hi,

you r right for 10Th question.

answer is 2:21

for 21 st question,

(2s-p)^2:(3t-p)^2=2s:3t it means(2s-p)^2/(3t-p)^2=2s/3t,use (a-b)^2=a^2+b^2-2ab,u get

(4s^2+p^2-4sp/9t^2+p^2-6tp)=2s/3t,do the cross multiplication

12ts^2+3tp^2-12spt=18st^2+2sp^2-12spt

12ts^2-18st^2=2sp^2-3tp^2

6st(2s-3t)=p^2(2s-3t)

6st=p^2

anyone know how to solve qustion no. 20 in this exercise?

@ avinash: Yes, Q.20 is damn easy once you know the concept behind "Sub Duplicate Ratio",
 For clarity, consider this- Sub duplicate ratio of a is a^{1/2}

Now according to Q. and above concept the equation becomes -

p^{2}/ q^{2} = [ p - x^{2}]/ [q - x^{2}]

After cross multiplication it becomes;

p^{2}q - p^{2}x^{2} = pq^{2} - q^{2}x^{2}

x^{2}[ p^{2} - q^{2} ] = p^{2}q - pq^{2}

After keeping x^{2} in LHS, we get;

x^{2} = [pq(p-q ] /  [(p-q)(p+q)]

x^{2} = pq/(p+q)

 Since this is not given in any of the options; answer is (d) that is None Of These

Hope you have got the concept and the problem  

One doubt regarding proportion solved example number 3  regarding tea powder.

I find it  wrongly solved.

Same pdf page 11.

it states profit is 17.5%.So if cost is 100 than 117.5 is sp and 17.5 is profit on it.

What they did is sp is 100 and 17.5 as profit.whereas 17.5 is percentage not amount and if cp is 85.1 than only sp can become 100 with 17.5 percent profit.

Am i right?