Brain Teasers
7, 17, 38, 81, ?
What goes next in this sequence?
7, 17, 38, 81, ?
7, 17, 38, 81, ?
Answer
168.The pattern is, *2+3, *2+4, *2+5, and the next one should be *2+6.
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Comments
Good one! I got the right answer, but the pattern I noticed was different. If you take the differences, you get 10, 21 and 43. Each of these differences is double the previous difference plus one. The difference between 38 and 81 is 43, double this plus one is 87, and 81 plus 87 is 168.
I noticed the pattern but miscalculated. My brain is faulty!
Sat there for a few minutes looking like .Then suddenly realised. Good one.
The Ninja, that, algebraically, is the same as Shenqiang's solution.
I got another answer : 157
If you take the difference between consecutive numbers you get the series :
10 21 43
The difference between the two numbers above is :
11 22.
I concluded that the difference between the diffrences is the multiple of 11. Consequently, the third number is 33.
The the fourth difference should be 43+33=76, resulting with 81+76=157.
If you take the difference between consecutive numbers you get the series :
10 21 43
The difference between the two numbers above is :
11 22.
I concluded that the difference between the diffrences is the multiple of 11. Consequently, the third number is 33.
The the fourth difference should be 43+33=76, resulting with 81+76=157.
Nice, but not very difficult.
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