Creating Zeroes*
Imagine purchasing 3 items costing P 13.55, P36.75 and P48.25 respectively. To know the total purchase, most people rely on the calculator in their cell phones. But there are techniques which can enable us to calculate in less time than when we try to get our calculator from our bags or pockets.
Creating zeroes in addition is one of them. There are three ways to create zeroes:
- Add number pairs or groups totalling to 10 or multiples of 10 first.
For example in finding the total of 3 + 4 + 6 + 8 + 5 + 9, we can add 4 and 6 first to get 10, then 3 , 8 and 9 will give 20. And 10 plus 20 plus 5 is easily 35.
- Mentally create zeroes by transferring. For example, in adding 47 and 23, we can mentally transfer the 3 in 23 to 47 to make it an even 50. 23 then becomes 20. And the addition becomes an easy 50 + 20 = 70.
- Add a round number first before deducting the excess. In adding 995 + 378, we can avoid the carries when adding from right to left which is the method taught in schools by simply adding a round number first.
995 is only 5 less than 1000 so we can add 1000 to 378 first, getting 1,378 and then deducting 5 to get 1373.
If we want to compute the total of our purchases at the start of this article, P13.55, P36.75 and P48.25, we can transfer the 0.25 from P48.25 to P36.75 to make it exactly P37.00. Then combine the P13 of P13.55 to P37 to make it a whole P50. We can then add P48 to P50 to make it P98 and finally attach the 0.55 from P13.55 to get a total of P98.55.
Try these!
- 3 + 9 + 4 + 7 + 6 =
- 7 + 7 + 8 + 3 + 6 + 5 =
- 98 + 67 =
- 48 + 76 + 52 =
- 74 + 68 + 46 =
- 636 + 583 + 364 =
- 597 + 388 =
- 989 + 789 =
- 2995 + 2345 =
- 599967 + 333333 =
See the answers in the next issue of the MATH-Inic Newsletter
*From Chapter 1 of 25 Math Short Cuts by Virgilio Y. Prudente
