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 April 11th, 2017, 02:15 AM #1 Newbie   Joined: Apr 2016 From: England Posts: 13 Thanks: 2 Working out numbers which are in both sequences. This question's really stumped me, and I can't seem to find any tutorials on how to answer it... The nth term of a sequence is 2n + 1 The nth term of a different sequence is 3n  1 Work out the three numbers that are in both sequences and between 20 and 40 Now the three numbers I managed to get are 25, 31 and 37 (as I assumed it meant the output of both of these sequences needs to be the same as well as being in between 20 and 40). For example 2x18+1= 37 as does 3x12+1= 37. Yet I still feel I'm going the wrong way around this. Many thanks in advance Last edited by skipjack; April 11th, 2017 at 04:05 AM.
April 11th, 2017, 02:45 AM   #2
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Quote:
 Originally Posted by WarmCustard This question's really stumped me, and I can't seem to find any tutorials on how to answer it... The nth term of a sequence is 2n + 1 The nth term of a different sequence is 3n  1 Work out the three numbers that are in both sequences and between 20 and 40 Now the three numbers I managed to get are 25, 31 and 37 (as I assumed it meant the output of both of these sequences needs to be the same as well as being in between 20 and 40). For example 2x18+1= 37 as does 3x12+1= 37. Yet I still feel I'm going the wrong way around this. Many thanks in advance
$2n+1$ will be all the odd numbers

$3n+1$ will be odd for $n$ even

the numbers with even index in the 2nd sequence between 20 and 40 are

25,31,37 as you discovered.

Last edited by skipjack; April 11th, 2017 at 04:06 AM.

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