Arithmetic operators MongoDB

• $add: Adds two or more numbers together. The $add operator can also concatenate strings.
• $subtract: Subtracts one number from another.
• $divide: Divides one number by another.
• $mod: Computes the remainder of dividing one number by another.
• $ceil: Rounds a number up to the nearest integer.
• $floor: Rounds a number down to the nearest integer.
• $abs: Computes the absolute value of a number.
• $sqrt: Computes the square root of a number.
• $pow: Raises a number to a specified power.
• $exp: Computes the natural exponential function of a number.
• $log: Computes the natural logarithm of a number.
• $ln: Computes the base-10 logarithm of a number.
  

Example

db.products.aggregate([
{ 
$project:{ 
product_name:1, 
price:1, 
quantity:1, 
total:{
$multiply:["$sale_price","$quantity"]
},
discount:{
$subtract:["$price","$sale_price"]} 
}  
}
])