ds: sequense

Question

can you pls explain the logic?

prep_gmat · Answer

D.

a1=10 a2 =5 .... you can find the number of terms greater than 1/2 for both statements.

mirhaque · Answer

I am a bit lost. How do you find elements in the series bigger than 1/2? please explain the logic.. thanx.

krisrini · Answer

I am not sure, but I think its C. 

Combing both statements together.

A(2) = 5 , A(1) -A(2) = 5 ==> A(1) = 10

Per defn A(n) = A(n-1)/n ==> A(3) = A(2)/3 or A(3) = 5/3 = 1.66

Simillarly A(4) = A(3)/4 ==> A(4) = 1.66/4 = .415

The series is a decreasing series, 10,5,1.66,.415,....

Hence I think C is the correct answer. Please let me know.

Thanks

MA · Answer

give that, An=A(n-1)/n. remember that if the above eq is true, 
A2=A1/2, A3=A2/3, A4=A3/4 and so on.........

from i, A2=5
A1/2=5
A1=10
If A1=10, A2=5, A3=5/3, A4=5/4 and so on.

from ii, A1-A2=5
A1-A1/n=5
A1-A1/2=5
2A1-A1 = 5
A1=10
If A1=10, A2=5, and as above....... hope that works.

krisrini · Answer

MA, you are absolutely correct with the solution,. 

However, there is a small mistake, A3 = A2/3 and hence A3 = 5/3 and not 5/2, same applies to A4 as well. But this doesn't matter in a DS question.

MA · Answer

thanx.. i am correcting the same/.

ds: sequense

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