If Ms. Anna and Mr. Mathew are children of Mrs. Smith, how many brothe

Hi,
The first sentence says Anna has same number of sis and bro, so the boys are one less than girls, as girls increase by one when Anna is also counted.
So s=b+1
So if we convert this info in terms of Mathews bro and sis...
Mathews brother are b-1, as Mathew himself is part of total b..
And sister is s..
As per statement ll, s=2(b-1)..... s=2b-2
Substitute s=b+1 in it..
b+1=2b-2...or b=3 And s =3+1=4..

Thanks a ton for the explanation Chetan. Cheers!

From Statement (1) alone, we have that Ms. Anna has the same number of brothers as sisters. If m is the number of male children Mrs. Smith has (so Anna has this many brothers), then she must have m sisters also. Hence, including Ms. Anna, Mrs. Smith must have m + 1 female children. Now, the number of children Mrs. Smith has equals m + (m + 1) = 2m + 1. But, we still do not know the value of m. Hence, Statement (1) alone is not sufficient.
From Statement (2) alone, we have that Mr. Mathew has twice as many sisters as brothers. Hence, if Mathew has, say, m – 1 brothers, then he must have 2(m – 1) sisters. Hence, the total number of children of Mrs. Smith equals m – 1 brothers of Mathew + 1 (Mathew himself) + 2(m – 1) sisters = m + 2(m – 1) = 3m – 2. Since we do not know the value m, Statement (2) alone is not sufficient.
Equating the number of children from both statements yields 2m + 1 = 3m – 2. Solving this equation for m yields m = 3. Hence, the number of children of Mrs. Smith is 2m + 1 = 2
3 + 1 = 7. Hence, the statements together answer the question.
The answer is (C).

My following approach is obviously incorrect - I am very happy to get your thoughts:

(1) Mr. Mathew is Anna's brother. If Anna has the same number of brothers and sisters, she has one more sister. Thus, 3 children all in all. SUFF

Hi chetan2u,

If in this calculation :

combined we have two eq and two variable so suff..
s+1=2(b-1)...
b=s..
so b+1=2(b-1)
b+1=2b-2... or b=3...
s=3..
therefore there are 4 sisters and 3 brothers.


from this we get s=3 and b=3. so shouldnt the total be 6 siblings?

HI,

We have taken the sisters of Ms Anna to be s, and we get s=b=3. Now, this s does not consider Ms Anna as a part of it.
But we are looking for total sisters and brother in the family, so now we have to include Ms Anna., so 3+1 sisters.

They both could have siblings on their respective father's side, so neither is sufficient. We only know they have the same mom.