# ✏️ 3.3.4.2 Whiteboard Practice

## Whiteboard Practice

When and how whiteboarding practice is implemented will be up to your teacher. Below is a recommended prompt.

### Goal

For this section's whiteboarding lesson, we’ll continue to practice with arrays, looping, and using C#'s basic operators (`+`

, `-`

, `*`

, `/`

, `%`

)

As the interviewee:

- Ask clarifying questions.
- Keep talking.
- Explain your plan at the beginning; recap what you’ve done at the end.
- Make eye contact.
- Plan your space.

As the interviewer:

- Answer questions as best as you can.
- Be encouraging. Whiteboarding is difficult!
- Be patient. Only offer hints if your partner indicates that they need help.
- Be engaged. Part of this practice is getting used to having someone evaluate your work as your produce it.
- Offer
*constructive*feedback. Find at least one thing that your partner did well*and*one thing they could improve at.

### Problem

**1st Prompt**: Write a method that returns a boolean indicating whether a number is prime. Recall that a number is prime if it is greater than 1 and is not evenly divisible by any other numbers excepting 1 and itself.

**Examples**:

Given: 7, Output: true

Given: 2, Output: true

Given: 8, Output: false

**2nd Prompt**: Write a method that returns an array of all of the multiples for a given number. A multiple of a given number is a number that can be multiplied by a second number to make the given number.

**Examples**:

Given: 7, Output: [ 1, 7 ]

Given: 24, Output: [ 1, 2, 3, 4, 6, 8, 12, 24 ]

### Further Exploration

Write a method that returns an array of all the prime numbers that are less than a given number.

**Examples**:Given: 7, Output: [ 2, 3, 5 ]

Given: 2, Output: [ ]

Write a method that returns the greatest common multiple (GCM) for two given numbers. The GCM is the largest number that both given numbers are evenly divisible by.

**Examples**:Given: 24, 18, Output: 6

Given: 50, 8, Output: 2

Given: 25, 5, Output: 5