Maths Calendar Trick - Sum of 9 numbers

The Calendar is something that we often look at almost everyday, for either planning our exams / meetings or holidays. But did you ever notice that you can play many cool tricks with it. One such trick is to calculate the sum of all 9 numbers selected on a calendar, in just 1 second. Let's see how it goes -

1. Draw a 3x3 box around any 9 numbers in the calendar. Let's say you had selected the 9 numbers as shown in the adjacent picture.

2. Now, multiply the middle number with 9. Here, it is 15 x 9 = 135

This result is nothing but sum of all the 9 numbers in the 3 x 3 box. That is 7 + 8 + 9 + 14 + 15 + 16 + 21 + 22 + 23 = 135

This trick works with any 9 numbers grouped in 3x3 box of the calendar. So, next time, ask you friend to select any 3x3 box in the calendar and amaze him by telling the sum of numbers while he is still calculating either manually or by calculator.