The result of division can usually be deduced through multiplication. Below are some tips for working with the figures:[br][br][list][*]If both numbers end in 0, then the numbers can be divided by 10.[/*][*]If both numbers are even, then the numbers can be divided by 2.[/*][*]If both numbers end in 5, then you can divide the numbers by 5.[/*][*]If one of the numbers ends in 0 and the other in 5, you can divide them by 5. [/*][*]If the sum of the digits of the number is divisible by three, then you can divide the number by 3.[/*][/list][br]Use these to continue to reduce the numbers, so you can deduce the result without a calculator. If you can't find anything in common, then there is nothing you can do about the bill. [br][br][color=#0000ff]Example 1:[/color] Calculate [math]72 \div 3.[/math][br][br][math]72 \div 3=\dfrac{72}{3}=\dfrac{8\cdot 9}{3}=\dfrac{8\cdot 3 \cdot \cancel 3}{\cancel 3}=8\cdot 3 =24.[/math][br] In [br]this example, the sum of the digits in the number 72 is 7+2 = 9, i.e. it is divisible by 3. [br][br][color=#0000ff]Example 2:[/color] Calculate [math]56 \div 16.[/math][br][br][math]56 \div 16=\dfrac{56}{16}=\dfrac{8\cdot 7}{8\cdot 2}=\dfrac{\cancel 8\cdot 7}{\cancel 8\cdot 2}=\dfrac{7}{2}.[/math][br][br]For large numbers, you should start with easy numbers, such as 2, 5 and 10, and proceed slowly. [br][br][color=#0000ff]Example 3:[/color] Calculate [math]420\div 20.[/math][br][br][math]420 \div 20=\dfrac{420}{20}=\dfrac{10\cdot 42}{2\cdot 10}=\dfrac{\cancel 10\cdot 42}{2\cdot \cancel 10}=\dfrac{6\cdot 7}{2}=\dfrac{\cancel 2\cdot 3\cdot 7}{\cancel 2}=3\cdot 7 = 21.[/math][br][br][color=#0000ff]Example 4: [/color]Calculate [math]4000\div 200.[/math][br][br][math]4000 \div 200=\dfrac{400}{20}=\dfrac{40}{2}= 20.[/math][br][br][color=#0000ff]Example 5:[/color] Calculate [math]1080\div 24.[/math][br][br][math]1080 \div 24=\dfrac{1080}{24}=\dfrac{2\cdot 540}{2\cdot 12}=\dfrac{\cancel 2\cdot 540}{\cancel 2\cdot 12}=\dfrac{2\cdot 270}{2\cdot 6}=\dfrac{\cancel 2\cdot 270}{\cancel 2\cdot 6}=\dfrac{2\cdot 135}{2\cdot 3}=\dfrac{\cancel 2\cdot 135}{\cancel 2\cdot 3}=\dfrac{5\cdot 27}{3}=\dfrac{5\cdot 3\cdot 9}{3}=\dfrac{5\cdot \cancel 3\cdot 9}{\cancel 3}=5\cdot 9=45.[/math][br][br]The examples do not try to take the calculations to the end result as quickly as possible, but show a conceptual Reducing the numbers gradually.