acenikk wrote:Jenny can write a software program in certain time. John can write the same program in 1/2 the time as Jenny takes. If they work together at their own rates, how many hours it take them to write the program ?

1. John can write the program alone in 3 hours.
2. If they work together then they take 1/3 of the time it takes Jenny alone to write the program.

Work rate of Jenny, WRf = 1/x
Work rate of John, WRm= 1/.5x

Q is (1/x)+(1/.5x)=?

With condition 1 we know .5x = 3 thus, sufficient.

Condition 2 states that (1/x)+(1/.5x)=1/y when y=(1/3)x, hence sufficient.

Therefore, IMO D.

acenikk wrote:Jenny can write a software program in certain time. John can write the same program in 1/2 the time as Jenny takes. If they work together at their own rates, how many hours it take them to write the program ?

1. John can write the program alone in 3 hours.
2. If they work together then they take 1/3 of the time it takes Jenny alone to write the program.

IMO A.

Statement 2 Doesn't give us value of the in time.

Answer is A.

Using a simple formula to calculate the combined time...

AB / (A + B) = T

Well represent Jenny's time using "Jen."

John's time is half of Jenny's, so we can call it ".5Jen."

Statement 1 -- SUFFICIENT
John takes 3 hours to write the program, half of Jenny's time. So Jenny takes 6 hours.

With the above, formula we can solve for the time it would take to write the program if both worked together:

(6*3)/(6+3) = 18/9 = 2 hours

Statement 2 -- INSUFFICIENT
If we look at the variables we created before diving into the statements, we see that statement 2 tells us nothing new.

(Jen * .5Jen)/(Jen + .5Jen) = (.5Jen^2)/1.5Jen = Jen/3

Jen/3 is one third the time it takes Jenny to write the program alone. Statement 2 is reiterating what we ALREADY KNOW.

Answer is therefore A.

OA is A... but I also got confused in the same way as "woo".

acenikk wrote:OA is A... but I also got confused in the same way as "woo".

just solve the equation by woo and you will see why you are confused:
his equation is
(1/x)+(1/.5x)=1/y when y=(1/3)x,
so substitute y=(1/3)x
1/x+ 2/x= 3/x
3/x=3/x. thats it. You can't solve it.
so You need to know that value of the time taken by either John or jenny or the total