Bobby and his younger brother Johnny have the same birthday. Johnny's

Hi,
A real GOOD Q worth the TAG 700 level..

To do this Q, you have to UNDERSTAND what it means...

Let the ages be..
Bobby Now= B
Bobby then=b
Johnny Now=J and
Johnny then=j..
1) Johnny's age now is the same as Bobby's age was when Johnny was half as old as Bobby is now
When johnny was half as old as bobby nwo... j=B/2..
what was bobby then : b, so J=b..
now the difference in Johnny's age then and now, and bobby's age then and now should be SAME, as same years have passed for both..
therefore J-j=B-b

Solution--

1) J-j=B-b
2) J=b, and
3) j=B/2
lets get all terms in values of B or b..
so
b-B/2=B-b..
2b=3B/2..

since we have ratios of all through above ratio, we require a NUMERIC value to find answer..

Lets see the statements
(1) Bobby is currently four times as old as he was when Johnny was born.
Just gives another ratio ... no NUMERIC value
Insuff

(2) Bobby was six years old when Johnny was born.
this gives us the difference in age of two J-B=j-b=6..
now j=B/2 so j-b=B/2-b=6..
or b=B/2 + 6..
Substitute this in our Equation 2b=3B/2..
so 2(B/2 + 6)=3B/2..
B+12=3B/2
or 2B+12*2=3B..
B=24..
Suff

B..

Of course, we can do a bit of intelligent guessing,
the Q gives us a ratio..

Statement 1 gives us another Ratio
so 1 cannot be suff on its own.. eliminate A and D..

Statement 2 gives you a numeric value..
Now you have a numeric value and a ratio..
in all likelihood we should get an answer, eliminate E....
betweenB and C, for the above mentioned reason you should be inclined towards B..
atleast you have got your probability of answering correctly to 1/2 from 1/5..[/b]

+1 kudos for good Q to you and to manhattan mgmat