Teachers and parents need to be aware of how knowledge of number sense shortcuts could not only motivate a love of learning mathematics, but impact problems you encounter in real life. Let me illustrate some examples. Example 1: When multiplying a number ending in 5 with an even number, double the number ending in 5, take half of the even number, and then multiply. 35 x 16 = 70 x 8 = 560.
Let’s use this shortcut in solving the following geometric problem. “Find the area of a rectangle with length 45 and width 14.” Since area is equal to length multiplied by the width, the area of the rectangle would be 45 x 14 = 90 x 7 = 630. Example 2: When multiplying a number by 25, divide the number by 4 and move the decimal point 2 places to the right. To solve 25 x 36, divide 36 by 4, which is 9, and then move the decimal point 2 places to the right. The answer is 900. Let’s assume that you want to find the cost of 24 cans of corn at 25¢ each. To solve, 25 x 24, divide 24 by 4, which is 6, then move the decimal 2 places to the right, the answer is 600¢, which is $6.00.
I have written instructional Number Sense workbooks for elementary, middle and high school students. Your child or student could benefit from mastering shortcuts for multiplying, subtracting, squaring, solving fractions, finding GCD, LCM or solving a variety of problems appearing in mathematics, from basic math to calculus. Number sense is not taught in public/private schools or colleges. I have been writing shortcuts for more than 50 years, so in that respect there is no one in the world that knows more about number sense than me. Visit the STORE to see what is available. The Magic of Mathematics will mesmerize you.