How to see it
A square number is a number times itself. Five fives make twenty-five, and it really is a square: five rows of five. A cube is a number times itself twice. Two times two times two is eight: a stack of two layers, each two by two. A root asks the question backwards.
A worked example
Square root of 625. Twenty squared is 400, too small. Thirty squared is 900, too big. So it is between twenty and thirty. And 625 ends in a five, so the root ends in a five. Twenty-five squared is 625.
The common mistake: halving instead of rooting
The trap is halving. Half of 625 is 312.5, and 312.5 times 312.5 is nowhere near 625. A root is not a half.
Try one
The square root of 225.
- A112.5
- B30
- C15
- D16
Show the answerHide the answer
Right: C, 15
Ten squared is a hundred, twenty squared is four hundred, and it ends in five.