Comparing, Rounding and Dividing Chapter Notes | Year 4 Mathematics IGCSE (Cambridge) - Class 4 PDF Download

Rounding, ordering and comparing whole numbers

• The objective is to round whole numbers to the nearest 10, 100, 1000, 10,000, or 100,000.
• Whole numbers can be ordered from smallest to largest or largest to smallest.
• Whole numbers can be compared using the signs =, <, and >.
• Rounding simplifies numbers for easier understanding, e.g., stating the distance from Jakarta to New York as roughly 16,000 km instead of 16,167 km.
• Rounding helps estimate answers before calculating, aiding in checking the sensibility of results.
• For example, to estimate 92 ÷ 4:
  • Round 92 to 80: 80 ÷ 4 = 20.
  • Round 92 to 100: 100 ÷ 4 = 25.
  • This suggests the answer to 92 ÷ 4 is between 20 and 25.
• Ordering numbers involves arranging them systematically, like arranging Russian dolls from shortest to tallest or numbers like 500, 505, 550, 555 in ascending order.

Division of 2-digit numbers

• The objective is to estimate the size of an answer when dividing a number up to 100 by a 1-digit number.
• Perform division of a number up to 100 by a 1-digit number.
• Decide whether to round up or round down after division to provide a sensible answer in context.
• Division involves splitting a quantity into equal parts or groups, such as sharing food fairly or organizing items.
• For example, to organize a party for 45 people with paper plates in packs of 8, divide 45 ÷ 8 and interpret the remainder to determine the number of packs needed.
• Estimation before division helps gauge the answer’s size, e.g., for 75 ÷ 4:
  • Round 75 to 80: 80 ÷ 4 = 20.
  • The answer is slightly less than 20.
• Division can be performed using methods like:
  • Number line: Count back in groups, e.g., for 75 ÷ 4, use 10 groups of 4 and 8 groups of 4, resulting in 75 ÷ 4 = 18 r3.
  • Repeated subtraction: Subtract groups of the divisor, e.g., for 75 ÷ 4, subtract 10 groups of 4 and 8 groups of 4, yielding 75 ÷ 4 = 18 r3.