Question

a teacher asked her students to design a cold pack. the desired criteria and constraints for the cold pack are as follows:

• it should be as cold as possible
• it should stay cold for about 5 minutes
• it should be reusable

the students were instructed to mix ammonium nitrate crystals in plastic bags filled with water. they were split into three groups, and each group created a design. each design used a different amount of ammonium nitrate crystals. the table shows the cold pack designs created by the three groups.

	temperature maintained (°c)	amount of time it stays cold (minutes)	reusability
design 2	3-5	3	twice
design 3	5-7	7	once

how could the designs be combined to best meet the criteria and constraints?

a. temperature maintained by design 2 and time design 1 stays cold
b. reusability of design 2 and temperature maintained by design 3
c. temperature maintained by design 1 and time design 3 stays cold
d. reusability of design 3 and time design 2 stays cold

Explanation:

The criteria are "as cold as possible", "stay cold ~5 minutes", and "reusable". Design 2 has the lowest temperature range (3-5°C, coldest), Design 1 stays cold for 5 minutes (matches the time requirement), and both Design 1 and 2 are reusable twice. Option A combines Design 2's cold temperature and Design 1's 5-minute cold duration, meeting all key criteria. Other options fail: B uses Design 3's higher temp (not coldest); C uses Design 1's warmer temp; D uses Design 3's single-use and Design 2's shorter time. Thus A is best.

Answer:

A. temperature maintained by Design 2 and time Design 1 stays cold