Chapter 14 Exam

A seller says 4 identical items at $19 each cost $95. Check that claim.

The assigned question is: “A seller says 4 identical items at $19 each cost $95. Check that claim.” A learner wrote: “19 × 4 = 77. I used this intermediate value to finish the assigned problem.” Identify a concrete invalid step or assumption. Work out the correct result and explain why it is valid.

Two pumps each deliver 20 L/min for 5 min. Find combined water output.

The assigned question is: “Two pumps each deliver 20 L/min for 5 min. Find combined water output.” A learner wrote: “I divided the stated rate into the time instead of multiplying rate by time for 20, and found 201 L.” Identify a concrete invalid step or assumption. Work out the correct result and explain why it is valid.

Two machines together produce 63 parts in 3 minutes at constant combined speed. Find their combined rate.

The assigned question is: “Two machines together produce 63 parts in 3 minutes at constant combined speed. Find their combined rate.” A learner wrote: “63 ÷ 3 = 22. I used this intermediate value to finish the assigned problem.” Identify a concrete invalid step or assumption. Work out the correct result and explain why it is valid.

A refill station made 88 L in 4 min. At the same rate, how much after one extra minute?

The assigned question is: “A refill station made 88 L in 4 min. At the same rate, how much after one extra minute?” A learner wrote: “I treated the constant rate involving 88 as the whole amount rather than amount per unit, and wrote 111 L.” Identify a concrete invalid step or assumption. Work out the correct result and explain why it is valid.