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Instructions

In this exercise you'll write code to analyze the production of an assembly line in a car factory. The assembly line's speed can range from 0 (off) to 10 (maximum).

At its lowest speed (1), 221 cars are produced each hour. The production increases linearly with the speed. So with the speed set to 4, the line should produce 4 * 221 = 884 cars per hour. However, higher speeds increase the likelihood that faulty cars are produced, which then have to be discarded.

You have four tasks.

1. Calculate the success rate

Implement the successRate() method to calculate the ratio of cars created without error for a given speed. Use comparisons to choose the correct rate from this table:

  • 0: 0% success rate (0.0)
  • 1 to 4: 100% success rate (1.0)
  • 5 to 8: 90% success rate (0.9)
  • 9: 80% success rate (0.8)
  • 10: 77% success rate (0.77)
<?php

$assembly_line = new CarsAssemble();
$assembly_line->successRate(10);
// => 0.77

2. Calculate the production rate per hour

Implement the productionRatePerHour() method to calculate how many cars are successfully produced per hour. Multiply the base production (221 cars per hour at speed 1) by the speed and by the success rate for that speed.

<?php

$assembly_line = new CarsAssemble();
$assembly_line->productionRatePerHour(6);
// => 1193.4

3. Check whether the line is running

Implement the isLineRunning() method to return whether the assembly line is running. The line is running when its speed is not identical to 0.

<?php

$assembly_line = new CarsAssemble();
$assembly_line->isLineRunning(0);
// => false

$assembly_line->isLineRunning(3);
// => true

4. Compare two line speeds

Implement the compareSpeeds() method to compare two speeds. It should return:

  • -1 when the first speed is less than the second
  • 0 when both speeds are equal
  • 1 when the first speed is greater than the second
<?php

$assembly_line = new CarsAssemble();
$assembly_line->compareSpeeds(3, 7);
// => -1

$assembly_line->compareSpeeds(5, 5);
// => 0

$assembly_line->compareSpeeds(9, 2);
// => 1