Question

Sal is trying to determine which cell phone and service plan to buy for his mother. The first phone costs $100 and $55 per month for unlimited usage. The second phone costs $150 and $51 per month for unlimited usage. How many months will it take for the second phone to be less expensive than the first phone?

Answer 1

It takes 13 months for the second phone to be less expensive than the first phone.

Explanation:

First phone: y = 100 + 55x

Second phone: y = 150 + 51x

(x = number of months, y = total cost)

Make a T-Chart.

First phone: Second phone:

x | y x | y

0 | 100 0 | 150

1 | 155 1 | 201

2 | 210 2 | 252

3 | 265 3 | 303

4 | 320 4 | 354

5 | 375 5 | 405

6 | 430 6 | 456

7 | 485 7 | 507

9 | 595 9 | 609

10 | 650 10 | 660

11 | 705 11 | 711

12 | 760 12 | 762

13 | 815 13 | 813

After 13 months, the second phone will have costed $2 less than the first phone, and the price of the second will continue to be lower than the first.

Answer 2

1st: 100+55x>150+51x

2nd: x>12.5

3rd: 13

Explanation: