Squaring of a number ending with 5

You can square numbers ending in 5 the same way you square other numbers. A quick way to square any number is by using a calculator; however, when you are squaring a two-digit number ending in 5, you can use an easy method without the aid of a calculator. For a two-digit number with the digit {\displaystyle x}

in the tens place, simply calculate {\displaystyle x(x+1)}

, then append 25 to the end of this product.

Set up the formula x(x+1){\displaystyle x(x+1)}

. Let {\displaystyle x}

equal the number being squared, excluding the 5 digit in the ones place.^[1] Plug this number into the formula.

1Separate the 5 from the rest of the number. You want to create two numbers: 5, and the number created by all the remaining digits in the number. This only applies to the 5 in the ones place, and not to other 5s that might appear elsewhere in the number.

For example, if you are squaring 65, you would create the number 6, and the number 5.
If you are squaring 115, you would create the number 11, and the number 5.

Set up the formula x(x+1){\displaystyle x(x+1)}

. Let {\displaystyle x}

equal the number being squared, excluding the 5 digit in the ones place.^[1] Plug this number into the formula.

For example, if you are calculating {\displaystyle 65^{2}}, {\displaystyle x=6}. Set up the formula as {\displaystyle 6(6+1)}, since 6 is the number you separated from the 5.
If you are calculating {\displaystyle 115^{2}}, {\displaystyle x=11}. Set up the formula as {\displaystyle 11(11+1)}, since 11 is the number you separated from the 5.