[PDF] 2013 Australian Mathematics Competition AMC Junior Years 7 and 8.pdf | Plain Text

Junior Division Questions 1 to 10, 3 marks each 1. 1999 + 24 is equal to (A) 1923 (B) 2003 (C) 2013 (D) 2023 (E) 2113 2. P QR is a straight line. Find the value of x. P Q Rx  10  20  30  (A) 40 (B) 90 (C) 100 (D) 110 (E) 120 3. The value of the fraction 1 2 is closest to (A) 0 :45 (B) 0.6 (C) 1 3 (D) 5 8 (E) 2 5 4. Which of the following is equal to 20? (A) 3 + 2 4 (B) (9 + 5) 2 4 2 (C) 10 2 (D) 20 + 20 2 (E) 10 2 5. How many minutes are there between 8:37 am and 10:16 am? (A) 39 (B) 79 (C) 99 (D) 141 (E) 179 6. Three squares each with an area of 25 cm 2 are placed side by side to form a rect- angle. The perimeter, in centimetres, of the rectangle is (A) 20 (B) 36 (C) 40 (D) 75 (E) 100 7. If every digit of a whole number is either a 3 or a 5, the number will always be (A) divisible by 3 (B) divisible by 5 (C) prime (D) even (E) odd 8. P is the point at 0 :56 and Qis the point at 1 :2 on a number line. The point which is halfway between Pand Qis at (A) 0 :34 (B) 0 :64 (C) 0 :83 (D) 0 :88 (E) 0.93

J 2 9. If triangle ABCis isosceles with 6 A = 40  , what are all of the possible values for 6 B ? (A) 40  (B) 40 and 70  (C) 40 and 100  (D) 70  and 100  (E) 40 , 70  and 100  10. In Gwen's classroom, the desks are arranged in a grid. Each row has the same number of desks. Gwen's desk is third from the front, second from the back and has one desk to the left and four to the right. How many desks are there? (A) 20 (B) 24 (C) 25 (D) 28 (E) 30 Questions 11 to 20, 4 marks each 11. William travels to school in two di erent ways. Either he walks to school and takes the bus home, or he takes the bus to school and walks home. In each case his total travelling time is 40 minutes. If he were to take the bus both ways, his total travelling time would be 20 minutes. How many minutes would it take if he walked both ways? (A) 30 (B) 40 (C) 50 (D) 60 (E) 80 12. The opposite faces on a standard dice add to give a total of 7. The game of Corners is played by rolling a dice and then choosing a vertex of the dice with your eyes closed. For example, the score for the vertex chosen below would be 4 + 5 + 6 = 15. Which of the following scores is NOT possible when playing Corners? (A) 6 (B) 7 (C) 8 (D) 9 (E) 10

J 3 13. A piece of paper in the shape of an equilateral triangle has one corner folded over, as shown. 40  x  What is the value of x? (A) 60 (B) 70 (C) 80 (D) 90 (E) 100 14. Beginning at the point A, Joel draws the spiral pattern of line segments below on a 1 cm grid. If he continues this pattern, how long, in centimetres, is the 97th segment? A (A) 46 (B) 47 (C) 48 (D) 49 (E) 50

J 4 15. Sixteen discs are arranged in four rows of four. The discs have a number on one side and are either red or green on the other. The number shows how many discs touching that disc have green on the other side. Row one Row two Row three Row four 1 2 1 2 2 1 4 0 0 4 0 2 2 0 2 0 Which of the following statements is true? (A) All of the rows have the same number of green discs. (B) Row one has more green discs than any other row. (C) Row two has more green discs than any other row. (D) Row three has fewer green discs than any other row. (E) Row four has fewer green discs than any other row. 16. While shopping this week I misread my shopping list and bought 5 loaves of bread and 2 bottles of milk. So I went back to the supermarket, got a full refund, and bought 2 loaves of bread and 5 bottles of milk. This cost me $4.20 less than my rst purchase. How do the prices of bread and milk compare? (A) A loaf of bread costs $1.40 more than a bottle of milk. (B) A loaf of bread costs $0.60 more than a bottle of milk. (C) A loaf of bread costs $0.42 more than a bottle of milk. (D) A loaf of bread costs $0.60 less than a bottle of milk. (E) A loaf of bread costs $1.40 less than a bottle of milk. 17. Starting with the number 0 on my calculator, I do a calculation in ve steps. At each step, I either add 1 or multiply by 2. What is the smallest number that cannot be the nal result? (A) 11 (B) 10 (C) 9 (D) 8 (E) 7

J 5 18. The three squares in the gure below are the same size. Find the value, in degrees, of 6 AM T . A B CD LM N S T (A) 45  (B) 50 (C) 55 (D) 60 (E) 75 19. Eight 1 1 square tiles are laid as shown. Two more 1 1 tiles are added, so that at least one side of each new tile is shared with a side of the original shape. Several di erent perimeter lengths are now possible. What is the sum of the shortest and longest possible perimeter of the modi ed shape? (A) 28 (B) 30 (C) 32 (D) 34 (E) 36 20. In the triangle P QR,S is a point on P Rsuch that P QSandS QR are both isosceles triangles (as shown). Angle QP Sis equal to angle S QR. j j j P Q RSx  x  What is the value of x? (A) 30 (B) 36 (C) 40 (D) 45 (E) 48

J 6 Questions 21 to 25, 5 marks each 21. A biologist has a set of cages in a 4 4 array. He wants to put one mouse (black or white) into each cage in such a way that each mouse has at least one neighbour of each colour (neighbouring cages share a common wall). The black mice are more expensive, so he wants to use as few of them as possible. What is the smallest number of black mice that he needs? (A) 4 (B) 5 (C) 6 (D) 7 (E) 8 22. Two discs have di erent numbers on each side as shown. 1 b c d The two sides of disc 1 The two sides of disc 2 The discs are ipped and they land on a table. The two numbers on the sides that are showing are added. If the possible sums that can be obtained in this way are 8, 9, 10 and 11, the sum b+ c+ dis (A) 8 (B) 18 (C) 20 (D) 27 (E) 30 23. An oddie number is a 3-digit number with all three digits odd. The number of oddie numbers divisible by 3 is (A) 20 (B) 26 (C) 29 (D) 41 (E) 42

J 7 24. Consider the following 4 4 squares with a 1 1 square deleted (shown in black). P Q R Consider tiling the squares P, Q and R using tiles like the one below. Which of the following statements is true? (A) Only P can be tiled this way. (B) Only Q can be tiled this way. (C) Only R can be tiled this way. (D) Only P and Q can be tiled this way. (E) All the shapes can be tiled this way. 25. A number is formed by writing the numbers 1 to 30 in order as shown. 12345678910111213::::::::::2930 Simeon removed 45 of these 51 digits leaving 6 in their original order to make the largest 6-digit number possible. What is the sum of the digits of this number? (A) 33 (B) 38 (C) 41 (D) 43 (E) 51 For questions 26 to 30, shade the answer as an integer from 0 to 999 in the space provided on the answer sheet. Question 26 is 6 marks, question 27 is 7 marks, question 28 is 8 marks, question 29 is 9 marks and question 30 is 10 marks. 26. Consider a sequence of letters where each letter is Aor B. We call the sequence stable if, when we tally the number of As and the number of Bs in the sequence, working from left to right, the di erence is never greater than one. For example, the sequence ABB ABAis stable but the sequence AABB ABis not, because after counting the rst two letters, the di erence is two. How many stable se- quences with eighteen letters are there?

J 8 27. Whenever Callum reads a date like 1 =8=2013, he incorrectly interprets it as two divisions, with the second one evaluated before the rst one: 1 (8 2013) = 251 5 8 For some dates, like this one, he does not get an integer, while for others, like 28 =7=2013, he gets 28 (7 2013) = 8052, an integer. How many dates this year (day/month/year) give him an integer? 28. What is the smallest positive integer that can be expressed as the sum of nine consecutive integers, the sum of ten consecutive integers and the sum of eleven consecutive integers? 29. Each of the four circles below has a whole number value. Xis the value of the top-left circle. A number written on the gure indicates the product of the values of the circles it lies within. What is the value of X+k? X 72 56 126 252k 30. Three di erent non-zero digits are used to form six di erent 3-digit numbers. The sum of ve of them is 3231. What is the sixth number?