Grade 8 The Number System Practice โ€” Hard

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Question 1 of 17: Is โˆš(2/9) rational or irrational?

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Answer key for parents & teachers (17 questions)
  1. Is โˆš(2/9) rational or irrational? โ€” Rational โ€” it equals โˆš2/3, and โˆš2/3 โ€ฆ wait, no. โˆš(2/9) = โˆš2/3 which is irrational. โˆš(2/9) = โˆš2/โˆš9 = โˆš2/3. Since โˆš2 is irrational and 3 is rational, the quotient is irrational.
  2. Which of these is a rational number between โˆš2 and โˆš3? โ€” 1.5. โˆš2 โ‰ˆ 1.414 and โˆš3 โ‰ˆ 1.732. The value 1.5 is between them and is clearly rational (= 3/2). โˆš2.5 is irrational.
  3. A student writes: "The decimal 0.123456789101112โ€ฆ is rational because it contains only digits." Are they correct? โ€” No โ€” the decimal is non-repeating and non-terminating, so it is irrational. The Champernowne-like decimal 0.1234โ€ฆ never enters a repeating cycle, making it irrational despite having a visible construction pattern.
  4. The number โˆ’โˆš2 is best classified as: โ€” Irrational. The negative sign does not change irrationality. โˆ’โˆš2 is still non-terminating and non-repeating, hence irrational.
  5. Between consecutive integers 4 and 5, which irrational number lies closest to 5? โ€” โˆš24. โˆš24 โ‰ˆ 4.899, โˆš17 โ‰ˆ 4.123, โˆš18 โ‰ˆ 4.243, โˆš20 โ‰ˆ 4.472. โˆš24 is closest to 5 among these choices.
  6. If p is rational and q is irrational, which expression is always irrational (assume p โ‰  0)? โ€” p + q. A nonzero rational plus an irrational is always irrational. p ร— p = pยฒ is rational; q ร— 0 = 0 is rational; p โˆ’ p = 0 is rational.
  7. What is the relationship between โˆšn and โˆš(n+1) for large positive integers n? โ€” โˆš(n+1) > โˆšn, but the difference gets smaller as n grows. Square roots are increasing but concave โ€” the gaps between consecutive square roots shrink as n grows larger.
  8. If 4.4ยฒ = 19.36 and 4.5ยฒ = 20.25, what is the best two-decimal approximation of โˆš20? โ€” 4.47. 4.47ยฒ = 19.9809 โ‰ˆ 20. Checking: 4.47 is between 4.44 (= 19.71) and 4.50 (= 20.25), and 4.47 is closest.
  9. Without a calculator, order these from least to greatest: โˆš5, 2.3, โˆš6, 2.5. โ€” โˆš5 < 2.3 < โˆš6 < 2.5. โˆš5 โ‰ˆ 2.236, โˆš6 โ‰ˆ 2.449. Order: โˆš5 โ‰ˆ 2.236 < 2.3 < โˆš6 โ‰ˆ 2.449 < 2.5.
  10. Which of the following is a correct strategy to estimate โˆšn to the hundredths? โ€” Squeeze between tenths: find a and a.1 such that aยฒ < n < (a.1)ยฒ, then try a.05. Systematic squeezing โ€” narrowing the interval by testing midpoints โ€” is the correct iterative approximation strategy.
  11. Using interval narrowing, a student finds 3.16ยฒ = 9.9856 and 3.17ยฒ = 10.0489. What is the best one-decimal approximation of โˆš10? โ€” 3.2. โˆš10 is between 3.16 and 3.17, so to the nearest tenth it rounds to 3.2.
  12. Which list correctly orders โˆš2, โˆš3, 1.5, and 1.8 from least to greatest? โ€” โˆš2 < 1.5 < โˆš3 < 1.8. โˆš2 โ‰ˆ 1.414, 1.5, โˆš3 โ‰ˆ 1.732, 1.8. So โˆš2 < 1.5 < โˆš3 < 1.8.
  13. Which statement about the real number system is FALSE? โ€” Real numbers are closed under division (any two reals can be divided). Division by zero is undefined. Since 0 is a real number and 5 รท 0 is undefined, the reals are NOT closed under division.
  14. If a is irrational and b is rational (b โ‰  0), is a/b rational or irrational? โ€” Irrational. Dividing an irrational by a nonzero rational always gives an irrational. E.g., โˆš2/3 is irrational.
  15. Which of the following does NOT follow from the field properties of real numbers? โ€” The sum of two primes is prime. 2 + 3 = 5 (both prime, prime result) but 2 + 7 = 9 (not prime). The other three are guaranteed field axioms.
  16. Between โˆš2 and โˆš3, how many rational numbers exist? โ€” Infinitely many. By the density property, infinitely many rational numbers exist between any two distinct reals.
  17. Which property is used in every step of solving the equation 3x + 6 = 15? โ€” Properties of equality combined with inverse and identity properties. Solving equations uses subtraction/addition (inverse) and division/multiplication (inverse) properties together with equality properties.