Answer:
Minimum number of messages to be sent is 251 for Plan A to be cheaper than Plan B.
Step-by-step explanation:
Let the text messages needed to be sent in order for Plan A to be cheaper than Plan B be N
Therefore total cost of sending text messages in case of Plan A is
[tex]C_A=\$ (30+0.01N)[/tex]
and total cost of sending text messages in case of Plan B is
[tex]C_B=\$ (20+0.05N)[/tex]
Now for Plan A to be cheaper than Plan B , [tex]C_A < C_B[/tex]
[tex]\therefore (30+0.01N)< (20+0.05N)=>N> 250[/tex]
Thus for Plan A to be cheaper than Plan B more than 250 messages needed to be sent . Minimum number of messages to be sent is 251 for Plan A to be cheaper than Plan B.