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Hi Stuart,Ian Stewart wrote:Good problem, and tricky- not one I've seen before.
1) If a_1 is 24, we have no way to know how many terms are less than 10. If k is positive, none of the terms will be less than 10, but if k is -1000, all of the terms besides a_1 will be less than 10. Insufficient.
2) If a_8 is 10, and k is positive, all of the terms after a_8 will be greater than 10, and all the terms before a_8 will be less than 10. So we would have 7 terms which are smaller than 10 (a_1 through a_7). If k is negative, the reverse will be true: all the terms after a_8 will be less than 10, and all the terms before a_8 will be greater than 10. Again, 7 terms are smaller than 10 (a_9 through a_15). So sufficient.
B.
Stuart is another expert on this forum, but I assume your question is directed to me. I'm afraid I don't understand your question, however. As described above, if you know that a_8 is 10, you know that exactly seven terms are larger than 10, and exactly seven terms are smaller than 10.anju wrote: Hi Stuart,
isn't the question asking about the number of terms in the sequence greater than 10. As per your explanation, we cannot have a value of terms which are greater than 10.
Let me know if i misunderstood your explanation.
Thnx
I am neither Stuart nor Mr.Stewart, but when you are evaluating (2), you cannot refer to the info in (1); you have to pretend that (1) doesn't exist. You should evaluate the statements in combination only if each of (1) and (2) are insufficient by themselves.NIXBTG wrote:hi Stuart - Should't the choices be consistent..
According to your explanation everything before a8 in the sequence is less than 10, however according the choice 1 of the question a1 = 21, which conflicts your explanation.
Also. it may be a stupid question, but i'm gonna ask.. can the series start from a with a large postive number and progressively reduce i.e. 24,22,20...10.... How can you assume that all terms before a8 are less than 10??
Thanks
nix
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