## Arthur Benjamin: A Performance of Mathemagic

You think you’re good in mental calculations? Watch Arthur Benjamin, one of the most amazing mental calculators of our time. Mr. Benjamin can square up to 4-digit number faster than a calculator. He can also square up to 5-digit numbers mentally. In addition, he can also determine mentally the day of the week that you are born.

Watch the 15-minute video of Mr. Benjamin the TED Talk titled Benjamin: A performance of Mathemagic.

Benjamin is the co-author of Secrets of Mental Math which is about the secret of rapid mental calculations. He is also the author of Proofs that Really Count: The Art of Combinatorial Proof .

## Number Word Problems 1 – How to Solve Number Problems Mentally

This is the first part of the Solving Number Problems Series for Grade 6-8 students, a-sub series of the Math Word Problem Solving Series.

Some of you probably need paper and pencil to solve number problems. You will be surprised that if you think harder and work backward, you can actually solve these problems in your head. Consider the following examples.

Example 1

One number is 1 more than the other. Their sum is 47. What are the numbers?

Explanation and Solution

First, one number is 1 more than the other. That means that if we subtract 1 from the larger number the two numbers will be equal. That’s our first clue.

Second, if we subtract 1 from the larger number, then we should also subtract 1 from the sum (Can you see why?). That makes the sum 46. Now, since the two numbers are equal, we can divide 46 by 2. That gives us 23 which is the smaller number. Now, since the other number is 1 larger than 23, then it is 24. 