Rossi is upgrading his cell phone in monthly service plan. Triax offers a new phone for $50 and a limited service for a monthly fee of $40. Cellular offers a new phone and unlimited service for a monthly fee of $50. After how many months will the cost of the two phones in monthly service fees be the same?

5 months

Step-by-step explanation:

Let n be the number of months.

1. Triax offers a new phone for $50 and a limited service for a monthly fee of $40. Then the phone will cost

$50+$40·n.

2. Cellular offers a new phone and unlimited service for a monthly fee of $50. Then the phone will cost

$50·n.

Equate these to amounts:

50+40n=50n,

50=50n-40n,

50=10n,

10n=50,

n=50:10,

n=5.