Back to Tutor Intake Assessment: Use rational approximations of irrational numbers

8.NS.A.2 Tutor Intake -- Rational Approximations of Irrational Numbers

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Grade 8·10 problems·~11 min·Common Core Math - Grade 8·container·8-ns-a-2
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A

Concepts

1

12=11^2 = 1 and 22=42^2 = 4. Since 1<2<41 < 2 < 4, what does this tell
us about 2\sqrt{2}?

2

A student says: "I can't plot 2\sqrt{2} on a number line because
we don't know its exact decimal value." Is this reasoning
correct?

3

A student tracks the error in approximating 2\sqrt{2}: at 1
decimal place the error is 0.04 (from 1.42=1.961.4^2 = 1.96); at 2
decimal places the error shrinks to 0.0119 (from
1.412=1.98811.41^2 = 1.9881). What happens to the error as more decimal
places are added?

4

A student writes "2=1.41\sqrt{2} = 1.41" on a worksheet. What is the
most accurate way to describe the problem with this statement?

B

Procedures

1

Approximate 3\sqrt{3} to the tenths place using the
squaring-and-narrowing technique. Given 1.72=2.891.7^2 = 2.89 and
1.82=3.241.8^2 = 3.24, enter the lower bound (the tenths value that is
too small).

2

Approximate 7\sqrt{7} to the hundredths place. Given that
2.642=6.96962.64^2 = 6.9696 (too small) and 2.652=7.02252.65^2 = 7.0225 (too big),
enter the upper bound.

3

Which is greater: 5\sqrt{5} or 7\sqrt{7}? Use that
5\sqrt{5} is between 2.2 and 2.3 (since 2.22=4.842.2^2 = 4.84 and
2.32=5.292.3^2 = 5.29), and 7\sqrt{7} is between 2.6 and 2.7 (since
2.62=6.762.6^2 = 6.76 and 2.72=7.292.7^2 = 7.29).

4

Estimate π2\pi^2 using π≈3.14\pi \approx 3.14. Compute 3.14×3.143.14 \times 3.14 and enter the result.

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