Dakota has four yardsticks

2022 Handbook

2022 Test A Math · Question 29 of 57

Question

Dakota has four yardsticks and two 12-inch rulers. If she lays all four of the yardsticks and both rulers end-to-end, what is the maximum number of feet she can measure accurately at once?

  • A12 ft
  • B14 ft
  • C16 ft
  • D18 ft
Show the answer

Correct answer: B

A yardstick is 1 yard in length.

1 yd=3 ft1\text{ yd} = 3\text{ ft}

4 yd=12 ft4\text{ yd} = 12\text{ ft}

A 12-inch ruler is 1 foot in length.

Two 12-inch rulers are 2 feet in length.

12 ft+2 ft=14 ft12\text{ ft} + 2\text{ ft} = 14\text{ ft}

Question analysis

Dakota lays four yardsticks and two 12-inch rulers end to end and wants to know how many feet she can measure at once. Students convert yards and inches to feet and add the lengths. Mixing up the units, or leaving out one kind of measuring stick, is the main risk in this unit conversion question.

NYS standards
  • 6.RP.3d converting measurement units
Grade level
Grade 6 content, by NYS standard
Compared with grade 7
Below grade 7 Converting yards and inches to feet is grade 6 measurement work. With friendly numbers and only two conversions to add, this is easier than typical grade 7 tasks, though the wording about measuring at once may slow some readers.
Estimated difficulty
Routine: one familiar step, little to misread.
What makes it hard
Solution
2 steps
Reading level
Question and choices: about grade 3, 37 words.
Corrected from the DOE handbook
  • A grammatical slip in the explanation was corrected.
Students, last 30 days
Not enough answers yet to show (it takes 10).
Why it is hard, traps and wrong answers (shows the answer)

Why it is hard

This is a unit conversion dressed as a measuring story: four yardsticks and two rulers are laid end to end, so the total is simply a sum of lengths. Points are lost by forgetting that the rulers count too, or by giving the rulers the yardsticks' length. Writing every piece in feet before adding, 3 + 3 + 3 + 3 + 1 + 1, shows the total at a glance.

  1. Something you must already know minor Working it out

    Neither conversion is given: a yardstick is 1 yard, or 3 feet, and each 12-inch ruler is 1 foot, so 4 yards and 24 inches become 12 + 2 feet. (Anderson & Krathwohl, 2001)

Strategy: Change every length to feet before adding: a yard is 3 feet and 12 inches is 1 foot. Then total the six pieces laid end to end.

Traps

  • Units or scale: The answer is wanted in other units, or a rate or scale must be converted first.
  • Stops one step early: A choice is a number from partway through the solution.

The wrong answers, classified

What was corrected from the DOE handbook, and why

  • Explanation: The handbook says “Two 12-inch rulers is 2 feet in length.” (p. 142, question 86), repeating the verb of the line before it, “A 12-inch ruler is 1 foot in length.” The site now reads “Two 12-inch rulers are 2 feet in length.” The working and the answer, 14 ft, are unchanged.

How the questions are analyzed, and the research behind it

Worked solution, step by step

Formulas used

Yards to feet
f=3×yf = 3 \times y
y is a length in yards. f is the same length in feet. One yard is 3 feet, so each yard adds 3 feet. A yardstick is exactly 1 yard long.
Inches to feet
f=i12f = \frac{i}{12}
i is a length in inches. f is the same length in feet. One foot is 12 inches, so divide the inches by 12. A 12-inch ruler is 1 foot long.
  1. Sort out the question

    Dakota lays 4 yardsticks and 2 rulers end to end, in one long line. End to end means each piece starts where the last one stops. So the total length is the sum of all six pieces. You need it in feet. A yardstick is 1 yard long. Each ruler is 12 inches long.

  2. Change the yardsticks to feet

    The four yardsticks make 4 yards.

    f=3×yf = 3 \times y

    f=3×4=12f = 3 \times 4 = 12

    The yardsticks make 12 feet. Watch out: don’t stop here. 12 feet is choice A, but the rulers count too.

  3. Change the rulers to feet

    Two rulers of 12 inches make 24 inches.

    f=i12=2412=2f = \frac{i}{12} = \frac{24}{12} = 2

    The rulers make 2 feet. Watch out: a ruler is not as long as a yardstick. Counting all six pieces as 3 feet gives 6×3=186 \times 3 = 18 feet, choice D.

  4. Add the lengths

    12+2=1412 + 2 = 14

    Dakota can measure 14 feet at once. So the answer is B, 14 ft.

Check your answer

List each piece in feet: 3+3+3+3+1+1=143 + 3 + 3 + 3 + 1 + 1 = 14. That matches. Or use inches. A yard is 36 inches, so 4 yards is 4×36=1444 \times 36 = 144 inches. Add the rulers: 144+24=168144 + 24 = 168 inches. Then 168÷12=14168 \div 12 = 14 feet.

The original DOE question

Question 86 as printed on page 86 of the DOE handbook.
As printed in the DOE’s NYC Guide to the Specialized High Schools Admissions Test (SHSAT) for 2023 Admissions, page 86, question 86. Open page 86 of the handbook (PDF) The handbook letters this question’s choices E–H; here they are A–D (E = A, F = B, G = C, H = D). This is the DOE’s version, before the corrections listed in the analysis.