Answer: See explanation
Step-by-step explanation:
Total number of text messages = 800
Amount used by Tommy and Mary = 1/2 × 800 = 400
Number of messages uses by Jack and Stefanie = 240
The expression to find the number of messages Cathy uses will be:
= 800 - (1/2 × 800) - 240
Since the expression is 800 - (1/2 × 800) - 240, the number of messages that Cathy will use will be:
= 800 - (1/2 × 800) - 240
= 800 - 400 - 240
= 160 messages
