Đề vòng chung kết Olympic TIMO 2020-2021 Khối 2 (Kèm đáp án)

 THAILAND INTERNATIONAL 
 MATHEMATICAL OLYMPIAD 
 FINAL ROUND 2020 – 2021 
 Primary 2 
 Time allowed: 120 minutes 
 Question Paper 
 Instructions to Contestants: 
1. Each contestant should have ONE Question-Answer Book which CANNOT be 
 taken away. 
2. There are 5 exam areas and 6 questions in each exam area. There are a total of 30 
 questions in this Question-Answer Book. Each question carries 5 marks. Total 
 score is 150 marks. No points are deducted for incorrect answers. 
3. All answers should be written on ANSWER SHEET. 
4. NO calculators can be used during the contest. 
5. All figures in the paper are not necessarily drawn to scale. 
6. Write down the answer in the simplest form. If the calculation result is a fraction, 
 please write down the answer as a proper or mixed fraction, decimal figure is also 
 accepted. Marks will NOT be given for incorrect unit. 
7. This Question-Answer Book will be collected at the end of the contest. 
 DO NOT turn over this Question-Answer Book without approval of the examiner. 
 Otherwise, contestant may be DISQUALIFIED. 
 1 
 All answers should be written on the ANSWER SHEET. 
 Arithmetic 
7. Find the value of 27+ 35 + 14 + 33 + 42 + 16 + 38 . 
8. If A and B are both 1-digit numbers, what is the value of BA− if the equation with 
 carrying is correct? 
 A 
 + A B 
 4 1 
 Question 8 
9. Find the value of 7 18 + 21 4 + 28 5. 
10. Find the value of 1−++−+−+−++ 2 1 3 4 5 6 7 8 ... 49 − 50 + 51 − 52 + 53. 
11. Find the value of 133831932323 +  +  −  −  . 
12. What is the number that should be filled in the blank if the equation below is correct? 
 32 = ___ 224 
 Number Theory 
13. The numbers below follow the arithmetic sequence, what is the 16th number? 
 246、239、232、225、218、 
14. Fill the lines with ‘ + ’ and ‘ – ’ to make the equation below correct. (Write down the 
 complete equation on the answer sheet) 
 18 7 9 4 = 16 
15. If A is an odd number, determine whether the result of AAA ( + 3 + 3 + 4) is an odd or 
 even number. 
16. In a math test, 11 students have an odd number of scores in total. The first 5 children have 
 an odd number of scores and another 5 children have an even number of scores. Does the 
 last student have an odd or even number of scores? 
17. How many 2-digit even number(s) that is / are multiples of 6 is / are there? 
18. Find the largest 4-digit number that is divisible by 10 without repeated digits. 
 3 
 All answers should be written on the ANSWER SHEET. 
 Combinatorics 
25. Among the following answers, how many 1- digit number(s) is / are there? 
 74+ , 35 , 17− 9 , 58+ , 36 6 , 14− 6 , 39+ 
26. Choose 2 digits, without repetition, from 3, 4, 1, 7 and 6 to form 2-digit numbers. Of 
 these 2-digit numbers, how many of them are even numbers? 
27. Choose 4 digits, without repetition, from 9, 1, 4 and 6 to form two 2-digit numbers. What 
 is the minimum value of the difference? 
28. How many 3-digit number(s) having the tens digit that is larger than 6 is / are there? 
29. It is known that every digit not smaller than the previous digit in a number is called 
 “special number”. For example, 123 and 366. How many 2-digit “special number” is / are 
 there? 
30. Alice has 11 $1 coins, 13 $2 coins and 4 $5 coins and a book costs $6. If she can only buy 
 1 book each time and no change will be provided for each payment, at most how many 
 book(s) can she buy? 
 ~ End of Paper ~ 
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