Arithmetic
Math, Mathematics
noun, の adjective
What is it called when you calculate numbers? That is the study of math and arithmetic.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
算数の先生は、田中先生です。
The teacher of arithmetic is Tanaka-sensei.
明日の算数のクラスに必要な道具は全部持ったの？
Do you have all the tools you need for tomorrow's arithmetic class?
算数のテストで答えが分からない時は、とりあえず一か四と答えておけば平気です。
If you don't know the answer on the arithmetic test, you can just say one or four and it'll be just fine.