Answer: 29;
2. Let 1, 3, 9, 27, 8 1, 243 be six given numbers, and you can get a new number by taking one number at a time from these six numbers or adding several different numbers (each number can only be taken once), so * * * gets 63 new numbers. If arranged in descending order, they are 1, 3, 4, 12, ... then the 60th number is ().
Answer: 360; Note: the title description is incorrect. Six numbers * * * can form 63 numbers. After sorting by size, there are 9 and 12 between 4 and 12.
For two-digit numbers, the number of the tenth digit is three times that of the first digit. If you subtract 9 from this two-digit number, the number of the first digit is equal to the number of the tenth digit. This two-digit number is ().
Answer: 31; Analysis: After subtracting 9, the tenth digit will decrease by 1 and the single digit will increase by 1. At this time, the numbers in the two digits are the same, which means that the original ten digits are two times larger than the numbers in the single digits, and because there is a three-fold relationship, it is easy to find the answer according to the sum-times relationship.
4. Calculate1001× 7 ÷ 37× 444 ÷137 = ().
Answer: 12
100 1×7÷37×444÷ 137
=(7× 137)÷7÷ 137×(4× 1 1 1) ÷37
=4×3
= 12
5. Calculate 22+42+62+...+402 = ()
Answer: 4240
Project number: (402-22) ÷20+ 1=20
And: (22+402)×20/2=4240.
6. There are three digits, and ten digits are the sum of one digit and one hundred digits. If you add 693 to this three-digit number, the hundred-digit number and the one-digit number will be exchanged. This three-digit number is ().
Answer: 198
7. The six-digit 865abc is divisible by 3, 4 and 5. In order to make 865abc as small as possible, a, b and c are () respectively.
Answer: A = 0, B = 2, C = 0；; (The title doesn't say that A, B and C can't be the same.)
8. The product of the numbers 7 1427 and 19 is divided by 7, and the remainder is (). 504 has () divisors.
Answer: 2; 24
9. A certain unit of the People's Liberation Army trains just in a phalanx. If 12 people are added to each row and 4 rows are reduced, it can be arranged in a rectangle. * * * There are () soldiers training in the queue.
Answer: 36
10. In the fifth-grade math competition, the product of Xiaoming's ranking multiplied by his age and competition results is 2 134, Xiaoming's ranking is () and his score is ().
Answer: 2; 97; (2 134=2× 1 1×97)
Thinking training II
1. There are four boxes of fruit. It is known that there are 42 apples, pears and oranges in each box and 36 pears, oranges and peaches in each box. Apples and peaches average 37 pounds per box. How many apples are there in the box? How many peaches are there in a box?
Answer:
42*3-36*3= 18
(37*2+ 18)/2=46 (pieces) ... Apple
46- 18=28 (pieces) ... peach trees
2. In an exam, the average scores of Party A, Party B and Party C are 9 1, Party B, Party C and Party D are 89, and Party A and Party D are 95. What are the scores of Party A and Party D respectively?
Answer:
9 1*3-89*3=6 (point)
(95*2+6)/2=98 (point) ...
98-6=92 (point) ... b
3. The average of five numbers is 18. After changing a number to 6, the average of these five numbers is 16. What is the original number of this change?
Answer: 16
( 18- 16)*5= 10
6+ 10= 16
4. Arrange five numbers from small to large, the average is 38, the average of the first three numbers is 27, the average of the last three numbers is 48, and what is the middle number?
Answer: 35
27*3+48*3-38*5=35
5. Find the average value of arithmetic progression 3,7, 1 1, ..., 643.
Answer: 323
Project number: (643-3)/4+1=161
Because the number of items is odd, the average value of the series is also an item in the middle of the series.
Average value: (3+643)/2=323
6. Xiaoming went up the mountain at a speed of 3 kilometers per hour, and when he came back, he went back at a speed of 5 kilometers per hour. What is the average speed of Xiao Ming's round trip?
Answer: 3.75 kilometers
Suppose the mountain road is 30 kilometers, and the average speed is:
30*2/(30/3+30/5)=3.75 (km)
7. There is a square lawn, and a one-meter wide path is built along the lawn, with a road surface area of 80 square meters. Find the lawn area.
Answer: 36 1 m2
80/4/ 1=20 (m2) 20- 1= 19 (m2) 19* 19=36 1 (m2)
There are six classes in Grade Five, and the number of students in each class is the same. Each class chooses 16 students to participate in the Young Pioneers activities, and the rest of the students are equivalent to the original four classes. How many students are there in each class?
Answer: 64 people
16*4=64 (person)
64/(5-4)=64 (person)
9. The sum of two digits of a two-digit number is 10. If the two digits of this two-digit number are reversed to form a new two-digit number, it will be 72 larger than the original number. Find the original two digits.
Answer: 19
72/9=8 (the difference between two numbers)
(10+8)/2 = 9 ... bits (the new number is greater than the original number)
10-9 = 1 ... Ten digits
The original number is 19.
10. A two-digit number, the number of the tenth digit is three times that of the first digit. If these two numbers are reversed to form a new two-digit number, and the difference with the original number is 54, find the original number.
Answer: 93
54/9=6 The difference between two numbers.
6/(3- 1) = 3 ... number.
3 * 3 = 9 ... The tenth digit.
The original number was 93.