A piece of cake
Definition 1 of 1
Pro Tip 1/3Informal Usage
Use 'a piece of cake' in casual conversations rather than formal or academic settings. 
Making friends at the new school was a piece of cake.
Pro Tip 2/3Cultural Nuance
The phrase is very common in American English and understood in most English-speaking cultures. 
Getting the team to agree was a piece of cake.
Pro Tip 3/3Positive Context
Use it to express a task completed with ease, often conveying a positive tone. 
Organizing the event was a piece of cake, thanks to the volunteers.