Can someone help with this?
I thought I was good with sequence questions but I had absolutely no idea what to do with this when I saw it.
Thanks!
gmat prep -sequence question
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Its a AP series.
Term = a + (n-1)d
where a = first term
n = nth term
d = difference
So here a =23, d=-3 and we need to find the nth term whose value is -4.
23+ (n-1)*-3 = -4
-3n+3 = -27
n = 10
Is the OA 10
Term = a + (n-1)d
where a = first term
n = nth term
d = difference
So here a =23, d=-3 and we need to find the nth term whose value is -4.
23+ (n-1)*-3 = -4
-3n+3 = -27
n = 10
Is the OA 10
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Thanks, but I don't understand what you meant here:
Term = a + (n-1)d
where a = first term
n = nth term
d = difference
So here a =23, d=-3 and we need to find the nth term whose value is -4.
How did you know the first term was 23?
Also, whats an AP? Arithmetic progression?
Thanks
Term = a + (n-1)d
where a = first term
n = nth term
d = difference
So here a =23, d=-3 and we need to find the nth term whose value is -4.
How did you know the first term was 23?
Also, whats an AP? Arithmetic progression?
Thanks
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I used the AP formula and did it manually
tn=t1 + (n-1)d
-4=23+(n-1)(-3)
n=10
23, 20, 17, 14, 11, 8, 5, 2, -1, -4 <----10th term
can't see how 14 is the answer (t1 would have to be 35 for n to be 14).
tn=t1 + (n-1)d
-4=23+(n-1)(-3)
n=10
23, 20, 17, 14, 11, 8, 5, 2, -1, -4 <----10th term
can't see how 14 is the answer (t1 would have to be 35 for n to be 14).
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But I'm still somewhat unclear as to this AP thing, especially this: tn=t1 + (n-1)d
where do I get more information on how to attack this?
thanks!
where do I get more information on how to attack this?
thanks!
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It's an arithmetic sequence. the question states that each consecutive term is 3 less than the previous.
for instance, the 3rd term would be 3 less than the second term, which is 3 less than the first term (hope thats clear)
1st term = 23
2nd term = 23-3 or 23+(1)(-3) = 20
3rd term = 23-3-3 or 23+(2)(-3) = 17
4th term = 23-3-3-3 or 23+(3)(-3) = 14
and so on...
To rewrite this into a formula, the value of the nth term would be 23+(n-1)(-3)
i.e. Value of nth term = 1st term + (n -1)(difference)
or
Tn = T1 + (n-1)d
for instance, the 3rd term would be 3 less than the second term, which is 3 less than the first term (hope thats clear)
1st term = 23
2nd term = 23-3 or 23+(1)(-3) = 20
3rd term = 23-3-3 or 23+(2)(-3) = 17
4th term = 23-3-3-3 or 23+(3)(-3) = 14
and so on...
To rewrite this into a formula, the value of the nth term would be 23+(n-1)(-3)
i.e. Value of nth term = 1st term + (n -1)(difference)
or
Tn = T1 + (n-1)d
Last edited by jrbrown2 on Wed Nov 21, 2007 10:34 am, edited 4 times in total.
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OOPS! forgive me! I didn't see that little comma that said T(1)=23!
For some reason, I thought that was a continuation from T(n)...
Now it makes sense, cos I was wondering how you determined that T(1)=23..
Thanks for your help!
(so can this formula be used for any sortof progression question?)
For some reason, I thought that was a continuation from T(n)...
Now it makes sense, cos I was wondering how you determined that T(1)=23..
Thanks for your help!
(so can this formula be used for any sortof progression question?)