The answers to the third question on page 46 of the supplementary exercises of mathematics in Volume 2 of grade 6

first
（12+8）x2
=20x2
=40 (m)
the second
20x3.14 = 62.8 (decimeter)

RELATED INFORMATIONS

1. A cuboid tank is 20 meters long, 15 meters wide and 2 meters deep. (1) the floor area of the tank? (2) the four walls and bottom of the tank are plastered with cement to calculate the area of cement? (3) how many tons of oil can be stored at most when the tank is used to store 0.85 tons of oil per cubic meter?
2. If both a and B are natural numbers that are not equal to 0, and three-quarters of a is equal to two-thirds of B, then () 1. Number a > number B 2. Number b > number a 3. Number a = number B
3. If 60% of a is equal to three fifths of B, and neither a nor B is equal to 0, then () 1. The number of a is greater than that of B 2. The number of a is less than that of B 3. Number a equals number B 4. Unable to determine
4. Number a plus 0.12 equals number B minus 0.12, number a () number B. A equals, B is greater than, C is less than
5. Multiple choice questions: if a, B and C are not equal to 0, and 1 of a + 1 of B + 1 of C = 1 of a + B + 1 of C, then a, B and C are three Number () A. There must be two opposite numbers. B. there must be two equal numbers. C. There must be the same sign. D. none of the above conclusions is correct
6. Given that a of B is two thirds and a is not equal to 2, find the value of A-B + 1 of a + B-5
7. Given a 6 = b 5 = C 4 ≠ 0 and a + b-2c = 3, the value of a is obtained
8. If 1 / 4 of a is equal to 1 / 5 of B, then a must be () B. (a, B are not zero) ① greater than ② less than ③ cannot be determined
9. If 2 / 5 of a is equal to 3 / 4 of B (A and B are not 0), then a: B=（
10. Judge whether a right triangle with a = 5 / 4, B = 3 / 4 and C = 1 is right triangle, and try to explain your reason
11. Solving binary linear equations: (substituting elimination method)! （1）{x-y=3,① （2 ）{2s=3t,① {3x-8y=14；② {s= 2t+5/3；②
12. Which two numbers multiply by two and add up to minus five which two numbers multiply by one and add up to minus five
13. Given the quadratic power of a = m, the quadratic power of B = n, find the value of (AB) 12 power (expressed by the algebraic formula containing m and N) （-2a)^3÷a^-2= 1.03×10^-4=
14. -Simple operation of 1-2-3 + 4 + 5 + 6-7-8-9 + 10 + 11 + 12 -. - 31-32-33 + 34 + 35 + 36 Quick, right away, good points! What seas, Straits and canals does a warship go through from the east coast of the United States to the Persian Gulf
15. A drawer of Mr. Wang's desk is 50cm long, 40cm wide and 12cm high. How many square decimeters of wood do you need to make this drawer?
16. The divisor is the divisor divided by the quotient. When the quotient is the remainder, what is the divisor equal to?
17. Find the volume of cylinder, cylinder, bottom diameter 0.6m, top diameter 0.7m, height 0.7m, what is the volume?
18. Divide the numbers of 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15 into five groups. The sum of three numbers in each group is equal to 24 What's the rule of doing this kind of problem?
19. Simple polynomial division by factorization (16x-1) divided by (4x ＾ + 1) divided by (2x-1)
20. X minus 7 and 4 / 5 is 4 and 2 / 7