Question

Difficulty: MediumSystems of Linear Equations

An online store sells two types of monthly subscription plans: a basic plan for 12permonthandapremiumplanfor12 per month and a premium plan for 20 per month. In April, the store had a total of 150 active subscribers for these two plans and collected a total of $2,280 in subscription fees. How many of the active subscribers in April were on the premium plan?

  1. A
    15
  2. B
    50
  3. 60Answer
  4. D
    90

Answer

60
By representing the number of basic subscribers as xx and premium subscribers as yy, we set up the system of equations x+y=150x + y = 150 and 12x+20y=228012x + 20y = 2280. Solving for xx in the first equation gives x=150yx = 150 - y. Substituting this into the second equation yields 12(150y)+20y=228012(150 - y) + 20y = 2280. Distributing the 12 and combining like terms gives 1800+8y=22801800 + 8y = 2280. Subtracting 1800 from both sides gives 8y=4808y = 480, and dividing by 8 results in y=60y = 60. Therefore, there were 60 premium subscribers.

Step-by-Step Solution

1
Define variables for the unknown quantities: let xx represent the number of basic subscribers and let yy represent the number of premium subscribers.
The system of equations is: x+y=150x + y = 150 and 12x+20y=228012x + 20y = 2280.
Translate the given information about total subscribers and total revenue into algebraic equations.
2
Express xx in terms of yy using the first equation (x=150yx = 150 - y) and substitute it into the second equation.
The substituted equation is: 12(150y)+20y=228012(150 - y) + 20y = 2280, which expands to 180012y+20y=22801800 - 12y + 20y = 2280.
Eliminate one variable to create a single equation with only one variable, yy.
3
Simplify the equation and isolate yy.
1800+8y=2280    8y=480    y=601800 + 8y = 2280 \implies 8y = 480 \implies y = 60.
Combine like terms and use basic operations to solve for the number of premium subscribers.

Key Concept

Solving a system of two linear equations using substitution or elimination.
Estimated Time:1m 30s
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