Tag Archives: multiplication by 2

MSC 9 – Dividing by 5, 50, 0.5, etc.

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:

  1. )     370 ÷ 5 =
  2. )     535 ÷ 5 =
  3. )     2,367 ÷ 5 =
  4. )     9,898 ÷ 5 =
  5. )     4,656 ÷ 50 =
  6. )     24,579 ÷ 50 =
  7. )     5,836 ÷ 500 =
  8. )     34,785 ÷ 500 =
  9. )     4,524 ÷ 0.5 =
  10. )    3,645 ÷ 0.05 =

Answers to all exercises are found in the answer key.

Discover the 25 Math Short Cuts ( 25 MSC )!