Question

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

• its temperature should remain at or above 90°c for as long as possible
• its temperature should remain as constant as possible
• it should be durable and leak proof
• it should fit inside shoes, gloves, or a pant pocket

the students were instructed to mix calcium chloride 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 calcium chloride crystals. the table shows the hot pack designs created by the three groups.

	amount of time at 90°c (minutes)	variation in temperature (°c)	durability of pack (hours)	size of pack
design 2	40	0 - 7	20	10 cm × 6 cm
design 3	30	0 - 7	15	8 cm × 5 cm

how could the designs be combined to best meet the criteria and constraints?
a. temperature variation of design 3 and size of design 2
b. time at 90°c of design 2 and durability of design 1
c. time at 90°c of design 3 and durability of design 1
d. temperature variation of design 2 and size of design 3

Explanation:

The desired criteria include maximum time at ≥90°C (Design 2 has the longest: 40 minutes) and maximum durability (Design 1 has the longest: 24 hours). These two features from Designs 2 and 1 best meet the key criteria. Other options either lack the longest time at 90°C or the highest durability.

Answer:

B. time at 90°C of Design 2 and durability of Design 1