Five (5) is ten divided by two ( 10 / 2 ), so to divide a number by 10/2, we
- multiply it by 2, then
- divide by 10.
Since dividing by 10 only involves moving the decimal point one place to the left, we can easily divide by 5 by just using doubling or multiplication by 2.
To divide a number by 5 we can either
Method A:
- double the number first then
- move the decimal point one place to the left.
Method B
- move the decimal point first then
- double the number.
We recommend the method B.
Let us try method A first.
Example 9.1: Find 164 ÷ 5
- Double 16 is 32 and double 4 is 8. So 164 x 2 is 328.
- Move the decimal point one place to the left to make it 32.8.
Now let us use the method B.
Example 9.2: Find 832 ÷ 5
- Shifting the decimal point of the multiplicand one place to the left will make it 83.2. This also fixed the decimal point for the answer.
- Doubling it gives 166.4.
Example 9.3: Find 1348 ÷ 50
- Since 50 is half of 100 or 102, we move the decimal point in 1348 two places to the left making it 13.48.
- We then double it to make it 26.96.
Example 9.4: Find 24.5 ÷ 0.5
- 0.5 is half of 1 or 100 so we do not have to adjust the decimal point. Just double the number to produce 49.0.
- The answer becomes obvious if we double both the dividend and the divisor: 24.5 ÷ 0.5 = 49.0 ÷ 1 = 49
Example 9.5: How many mint candies costing 50 centavos each can I buy with P 24.50?
The figures here are the same as in Example 9.4 and the solution here clarifies the technique we used earlier: We can buy 2 candies for one peso; so for 24.50 pesos we can buy 24.5 x 2 or 49 candies.
Example 9.6: Find 376 ÷ 0.05
- 0.05 is half of 0.1 or 10-1so we have to move the decimal point one place to the right, meaning we have to add a zero making it 3,760.
- Doubling it would result to 7,520.
Exercise 9: Compute the following:
- ) 370 ÷ 5 =
- ) 535 ÷ 5 =
- ) 2,367 ÷ 5 =
- ) 9,898 ÷ 5 =
- ) 4,656 ÷ 50 =
- ) 24,579 ÷ 50 =
- ) 5,836 ÷ 500 =
- ) 34,785 ÷ 500 =
- ) 4,524 ÷ 0.5 =
- ) 3,645 ÷ 0.05 =
Answers to all exercises are found in the answer key.
Discover the 25 Math Short Cuts ( 25 MSC )!
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