write the trick to find square of number with unit digit 5 and 1
Answers
Answer:
To square a number ending in 5, take the digit(s) to the left of the 5:
Take the digits to the left of the 5.
Treat those digits as a separate number. We’ll call it n
Multiply n×(n+1) .
Append the digits 25 to the end of your result.
Let’s look at a few examples:
Calculate the square of 75.
The digit to the left of 5 is 7. Multiply 7 by (7+1), or 8. 7 times 8 is 56. The answer is 5625.
Calculate the square of 115.
The digits to the left of 5 are 11. Multiply 11 by (11+1), or 12. 11 times 12 is 132. The answer is 13225.
Calculate the square of 265.
The digits to the left of 5 are 26. Multiply 26 by (26+1), or 27. 26 times 27 is 702. The answer is 70225.
This works for any number whose units digit is 5; however, the “trick” becomes substantially harder to perform in your head as the numbers get larger. A mental math trick that requires the use of a calculator isn’t very useful if the whole purpose of the trick was to avoid the use of a calculator in the first place.