Average Book Value Formula

I need someone with a mathematical background for help on 3 math problems please! SHOW YOUR WORK PLEASE!!!!!?
The answers need to be step by step please! I do not want just the answer but how to do it and how you used the formula (if you used a formula). Thank You in advanced. I really want to learn how to do this!!
1) A book has 600 pages and is numbered 1,2,3 and so on. How many times does the digit 7 appear in the page numbers?
2) In three bowling games, Miguel scores 129, 133, and 154. What score will Miguel need in a fourth game in order to have an average score of 165 for all four games?
3) A and B represent numbers, and A*B means (A+B)/2. What is the value of 3*(10*8)?
1)
This one is simply just counting them then multiplying:
for double digits: 07, 17, 27, 37, 47, 57, 67, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 87, 97
total 7′s=20 (2 are in 77)
Note this will continue for all 100′s, so you have them for the 0xx, 1xx, 2xx, 3xx, 4xx, and 5xx.
Since there are 6 times this cycle occurs, you multiply it by 6:
6*20=120
2)
The equation for mean is:
(sum of all tries)/(amount of tries)=(Average)
(129+133+154+x)/4=165
129+133+154+x=660
416+x=660
x=244
3)
This one doesn’t make much sense. Is it just asking for the product of 3*10*8? if so, 240.
Maybe I’m reading it wrong and it is supposed to be worked like this:
First we have 3*(10*8), so
A=10
B=8
since they are multiplied together, they are but in the (A+B)/2 equation:
(10+8)/2=9
Now we have 3*9, so
A=3
B=9
plug into equation:
(3+9)/2=6
so 6?
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