These questions are to be solved without a calculator:

1) Three different non-zero digits are used to form six different 3 digit numbers. The sum of 5 of them is 3321. What is the 6th number?

2) How many pairs \((a, b)\) of positive integers are there such that \(a\) and \(b\) are factors of \(6^6\) and \(a\) is a factor of \(b\)?

3) All digits of the positive integer \(N \)are either \(0\) or \(1\). The remainder after dividing\( N\) by \(37\) is \(18\). What is the smallest number of times that the digit \(1\) can appear in \(N\)?

4) In how many ways can the numbers 1, 2, 3, 4, 5, 6 be arranged in a row so that the product of any 2 adjacent numbers is even? Choices are: 64 or 72 or 120 or 144 or 720

5) A hockey game between two teams is 'relatively close' if the number of goals scored by the two teams differs by more than two. In how many can the first 12 goals of a game is scored if the game is "relatively close"?

6) The 4 digit number \(pqrs\) has the property \(pqrs \times srqp\). If \(p = 2\) what is the value of the 3 digit number \(qrs\)?

7) If \(x^2 = x + 3\), then what is the value of \(x^3\)? Choices are: A) x + 6 B) 2x + 6 C) 3x + 9 D) 4x + 3 E) 27x + 9

Please answer these questions with complete steps in the comment section below. I thank everyone who tries from the bottom of my heart.

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## Comments

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TopNewest1) Call the digits a,b,c. The sum of all six 3-digit numbers is 222(a+b+c). 222(a+b+c)-3321=the 6th number. Call it 100c+10b+a. A table of 222n-3321 show when n=18 yields 675 whose digits sum to 18. So the 6th number is 675.

2) \(6^{6}=2^{6}3^{6}\) which has \(7\cdot 7=49\) factors. So there are 49 possible values of b. You can use the same trick to find the number of a for each b. The total is \(1+2+3+4+5+6+7)+(2+4+...14)+...+(7+14+...+49) = 28\cdot28 = 784 \)

3) \(10^n\) has only three possible remainders: 1, 10, 26. You seek to make a sum of 18. 26*2-37=15 which is really close, just need three 1's: The smallest arrangement is 1101101 and the answer is 5.

4) The odds must be separated. Considering just even/odd there are 4 arrangements: oeoeoe, oeoeeo, oeeoeo, eoeoeo. There are 3!=6 ways to place the odds and 3!=6 ways to place the evens. \(4\cdot6\cdot6=144\).

5) Makes no sense. I think maybe you mean 'relatively close' means they never differ by 2 (or maybe at most 2) and you want the ways the game can remain relatively close with 12 goals scored.

6) Seems to be missing the property.

7) Multiply by \(x\) to get \(x^{3}=x^{2}+3x\) then sub in the given \(x^{2}=x+3\) and simplify to \(x^{3}=4x+3\)

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For Q2, how did you find it has 49 factors .

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To count the number of factors a number has, look at its prime factorization. Then add 1 to each exponent and multiply them together.

For example \(360=2^{3}3^{2}5^{1}\) and has \(4 \cdot 3 \cdot 2 = 24\) factors.

\(6^{6}=(2 \cdot 3)^{6} = 2^{6}3^{6}\) and has \(7 \cdot 7 = 49\) factors.

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\(2^{m-1}3^{n-1}\) (\(m\in\{1,2,3,4,5,6,7\},n\in\{1,2,3,4,5,6,7\}\)), and \(2^m3^n\) has \(mn\) factors.

The sum of all the possibilities of \(m\) is \(1+2+3+4+5+6+7\). The sum of all the possibilities of \(n\) is also \(1+2+3+4+5+6+7\).

So, the sum of the possibilities of \(mn\) equals \((1+2+3+4+5+6+7)(1+2+3+4+5+6+7)=784\)

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this

You can viewThe factors of \(2^63^6\) is in the form of \(2^m3^n\), so \(m\in\{0,1,2,3,4,5,6\},n\in\{0,1,2,3,4,5,6\}\), hence there are \(7\times7\) possibilities of \(2^m3^n\)

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Can you re-give your answers somewhat more detailed for a grade 9 student? please for Q1, Q2, and Q3 only

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For (Q1) you mentioned, "a table of 222n -3321"; how am I going to get a table from as it is a non-calculator question

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Good question, but it really isn't that hard to make a table for these numbers without a calculator, even though I used one.

You can do 222*15=3330 in your head. 3330-3321=9 then just count by 222's. (15, 9) (16, 231) (17, 453) (18, 675)

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Q1 If the sixth number is \(\overline{abc}\), then \(3321 + \overline{abc} = 222(a+b+c)\). The smallest number that can be added to \(3321\) to give a multiple of \(222\) is \(9\), but \(009\) does not contain \(3\) distinct digits. Other possibilities of \(\overline{abc}\) are \(9+222k\), in which case \(a+b+c = 15+k\). A but of trial and error leads you to \(k=3\) and \(\overline{abc} = 675\).

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For Q1, call them a,b,c so one number is 100a + 10b + c, 100a + 10c + b etc. Add all 6 up to get 222(a + b + c). Think from here

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I got stuck right from here... :(

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Q6 :Perhaps you mean pqrs=4*srqp?(2178x4=8712)

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Yes but how did you find that number without trial and error as calculator isn't allowed

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This is one of the problems on brilliant.You can view the solution here

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For Q4, to avoid consecutive odd digits, the even digits must be either in positions 2,4,6 or 1,3,5. There are 3! * 3! ways for each case so 72

(also don't undertand Q6)

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not quite. Evens can also be in 2,4,5 or 2,3,5 because they can be next to each other.

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oh yeah

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For Q7, multiply all by x and then sub in the value of x^2 from what is given

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