Math: Number sequence question?

Mark,I've got the first,third,fifth and sixth questions..

I'll try doing the others too.But for now,I have been able to get only those.Comment below if you have any doubts.

1st question-->6x+8

i.e.,the number multiplied by 6 then added by 8.The first number,2 multiplied by 6 gives 12,12+8 gives 20.

(20 multiplied by 6)+8 gives 128.(128x6)+8 gives 776.(776x6)+8 gives 4664.

3rd question--> x+1/2x

i.e.,16+half of 16 is the next number which is 24,then,24+half of 24 is the next number which is 36.Finally 54+half of 54 is 54+27=81

5th question--> -10x+1

i.e.,each number is multiplied by (-10) and 1 is added to the result.The first number,18,multiplied by -10 is -180, -180+1=-179, -179 multiplied by -10 is 1790,1790+1=1791,then, 1791x(-10) is -17910,-17910+1=-17909

6th question--->7^1,7^(1x2),7^(2x2),7^(4x2)

i.e.,7 raised to its first power,then,the powers are multiplied each time by a factor of 2 sequentially.

7^1=7,then,1 is multiplied by 2 to get 7^2=49,then,2 is multiplied by 2 to get 7^4=2401,then, 4 is multiplied by 2 to get 7^8=5764801 (the powers are sequentially multiplied by 2)

Yahoo answers would not let me post the question under details for some weird reason...

I am writing an aptitude test in about a months’ time and have been working though all sorts of online tests.

One part of the test involves number sequences which I usually score around 80%. There are a few sequences though that I am having difficulty answering and am wondering if someone can point out the pattern to solve these sequences?

The more patterns I am familiar with going into the test the more options I will have at my disposal.

Please explain what pattern you found when solving the problem (even if you answer just one question that is appreciated).

I will post the answers beside the questions.

Thanks in advance.

Out of the 35 practice questions I have written so far these are the six that I have gotten wrong:

2, 20, 128, ???, 4664 Answer: 776

1, 4, ??, 172, 1,201 Answer: 25

16, 24, 36, 54, ?? Answer: 81

2, 1, -4, -7, -10, ? Answer: +13

18, -179, ? , -17909 Answer: +1791

7, 49, 2401, ? Answer: 5764801

This is the famous Fibonacci Sequence. Each number is the sum of the two previous numbers (1+1=2, 1+2=3, 2+3=5, 3+5=8) So, to continue you would add the last two numbers, 5 and 8, to get 13 1, 1, 2, 3, 5, 8, 13 Add the last two again, 8+13 = 21 1, 1, 2, 3, 5, 8, 13, 21 Just keep adding the last two numbers to get the next number.

second Question: multiply the number by 7 then minus by 3:

(1*7)-3=4 , (4*7)-3=25 , (25 *7)-3=172, (172*7)-3=1201