Dividing a number by 2 is also called halving. This is a very important skill that all students should develop early. Halving can be used also in dividing by 4 and by 8 and also in multiplying by 5, 25 and 125.
Since young children can easily learn and master the 2 times table, they can mentally halve even numbers less than 20. Halving large numbers then, can be easily done by splitting them into smaller more manageable parts as discussed in our “25 Math Short Cuts” book which has over 10,000 copies in circulation. (Our books are not available in bookstores but you can order them through our “MATH-Inic Philippines – Math Made Fun, Fast and Easy” Facebook page.)
If all the digits of the number are even, then we can halve digit by digit from the left and immediately announce the answer.
However, if some of the digits are odd, we have to pair them with the following even numbers.
Halving 647, 052 can be done mentally using the following steps:
- Read the dividend first: six hundred forty-seven thousand, fifty-two to know the place values of the digits in the answer.
- Half of six hundred is three hundred
- Half of forty is twenty
- 7 is odd so we will group it with the next digit, 0, which is even. Half of seventy is half of sixty plus half of 10. Thus three thousand , five hundred
- 5 is odd so we will pair it with the ending 2. Half of 52 is half of forty plus half of 12. Thus we have twenty six.
An alternative solution is one we can use to perform short division, which we will discuss in a future post. After steps a to c, we have
d) half of seven is three thousand remainder 1
e) place the remainder 1 in front of the next digit 0 to make 10 the next dividend. Half of 10 is five hundred
f) Half of 5 is 2 (twenty) remainder 1.
g) use 1 as prefix of the last digit 2 to make 12. Half of 12 is six.
Practice by halving each of the following:
- 563, 458
- 752, 356
Answers to last week’s exercises. Find the digit sums of the following by casting out 9s:
- 923 → 5
- 567 → 0
- 838 → 1
- 5,437 → 1
- 9,897 → 6
- 6, 789 → 3
- (123 x 345) → 0
- (4589 x 9281) → 7
- (123 + 456 + 789) → 0
- ( 23 x 592 + 785) → 1
We are inviting you to join us in our Vedic Math activities this year: https://www.math-inic.com/blog/revised-schedule-of-vedic-math-activities-in-the-philippines/