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Đề thi toán Kangaroo Canada lớp 7-8 năm 2007

Đề thi toán Kangaroo Canada lớp 7-8 năm 2007

1. Part A: Each correct answer is worth 3 points.

What is the value of the expression: ?

2. A robot starts walking on the table from square A2 at the direction of the arrow, as shown on the picture. It always goes forward. If it reaches a barrier, it always turns right. The robot will stop if he cannot go forward after turning right. On which squ are will it stop?

3. Rose bushes were planted in a row, 2 m apart, on both sides of a road. How many bushes were planted along 20 m of the road?

4. A regular die has a total of 7 points on any two of its opposite faces. On the figure, two regular dice are placed, as shown. What is the sum of the points on all invisible faces of the dice?

5. The points A(2006, 2007), B(2007, 2006), C(-2006, -2007), D(2006, -2007), and E(2007, - 2006) are plotted on a co-ordinate grid. Which of the segments is horizontal?

6. A small square is inscribed in a big one, as shown in the figure. The lengths of two of the segments are given (3 units a nd 5 units). What is the area (in square units) of the small square?

7. The figure on the right is composed of white and black unit squares. What is the least number of white squares to paint black for the figure to obtain a line of symmetry?

8. A number is called “palindrome” if it reads the same backwards as forwards. For example, 13931 is a palindrome. What is the difference betwe en the least 5-digit palindrome number and the greatest 6-digit palindrome number?

9. Part B: Each correct answer is worth 4 points.

Six identical circles are arranged, as shown on the figure. The circles touch he sides of a large rectangle as well as each other. The vertices of the small rectangle coincide with the centres of four of the circles. The perimeter of the small rectangle is 60 cm. What is the perimeter of the large rectangle?

10. The squares on the figure are formed by intersectin g the segment AB by the broken line AA1A2 ...A12 B. The length of AB is 24 cm. What is the length of th e broken line AA1A2 ...A12B?

11. If x denotes any negative integer number, which of the following expressions will always have the greatest value?

12. Six points are chosen on two parallel lines x and y, as follows: 4 points are on line x and two points are on line y . How many triangles with their vertices among the given points are there?

13. Five integer numbers are written around a circle in a way that no two or three adjacent numbers have a sum divisible by 3. How many of the se five numbers are divisible by 3?

14. In the figure, ABC and CDE are congruent equilatera l triangles. If the measure of the angle ACD is 80° , what is the measure of angle ABD?

15. What percent of all natural numbers from 1 to 10000 are perfect squares? ( Perfect square is a number that can be presented as a square of a natural number, for instance 100 = 102 ).

16. By drawing 9 lines (5 horizontal and 4 vertical) Pe ter can construct a table with 12 cells. If he had used 6 horizontal an d 3 vertical lines, he would have constructed a table with 10 cells only. At most how many cells will there be in a table constructed by a tot al of 15 lines?

17. Part C: Each correct answer is worth 5 points.

A survey found that in 2006, 2/3 of all customers preferred product A, and 1/3 of all customers preferred product B. After a media campaign that promoted product B, a new survey in 2007 showed that ¼ of the customers who  reviously preferred product A are now buying product B. Which of the following statements is definitely true?

18. The segments OA, OB, OC, and OD are constructed from the centre O of the square KLMN to its sides, so that OA ⊥ OB and OC ⊥ OD (see the figure). The side of the square is 2. What is the total area of the shaded regions?

19. A broken calculator does not display the digit 1. F or example, if we type in the number 3131, only the number 33 is displayed, with no spaces. Mike typed a 6-digit number into this calculator, but only 2007 appeared on the display. How many numbers could have Mike typed?

20. It takes Angie 2 hours round trip to walk a tour th at contains a horizontal section and a slope section. On the way there she walks up hill on the slope section, and on the way back, she walks down hill on the same section. If Angie’s speed is 4 km/h on the flat section, 3 km/h climbing and 6 km/h going down, what is the total distance of the tour (round trip)?

21. The first digit of a 4 –digit number is equal to the number of zeroes in this number. The second digit of the number is equal to the number o f digits 1, the third digit is equal to the number of digits 2, and the fourth digit represents the number of digits 3 in this number. How many numbers have this property?

22. The table 3 × 3 contains nine natural numbers (see the picture). Nick and Peter erased four numbers each so that the sum of t he numbers erased by Nick was three times as great as the sum of the num bers erased by Peter. What number remained in the table?

23. On the picture, you can see a square tile, 20 cm × 20 cm. The design on the tile consists of two arcs of circles, as shown. If a table top with dimensions 80 cm × 80 cm is to be covered by these tiles so that some arcs connect in a curved line, what could be the maximum length of th is line?

24. A three – digit number has been divided by 9. The s um of the digits of the result was 9 less than the sum of the digits of the number. For how m any three-digit numbers would this be true?