Estimating money | Year 4 Mathematics PDF Download

Estimating Costs

In estimating costs, it's often simpler to round to the nearest whole unit instead of dealing with fractions of that unit. This method can help us quickly gauge approximate expenses.

Examples

Example 1: Joe orders a slice of cake costing £3.80.
What is £3.80 rounded to the nearest pound?
Sol: We're going to use a number line to see if £3.80 should be rounded up or rounded down.
This number line has been labelled with the nearest pounds on either end and each mark on the number line represents 10p.
To round £3.80 to the nearest pound we place it on a number line.
Whichever whole number it is closer to on the number line is the number we round it to.

Example 2: Knowing how to estimate costs is useful when we are shopping and need to check if we have enough money.
Joe is shopping for food for his packed lunch and this is the cost of items in his local supermarket.

What is the cost of the cheese and the cake to the nearest pound?
Sol: For both of these items we round up because they both have tenths above 5.
Cheese = £4
Eggs = £2
Now we’ve rounded the cost of the cheese and eggs to the nearest pound, what is the approximate total cost of the cheese and eggs?
4 + 2 = £6

Calculating change

• Estimating costs helps determine how much change Joe will receive.
• Joe wants to buy strawberries, crisps, and melon.
• First, round the items to the nearest pound:
  • Strawberries: £3.50 (rounds to £4)
  • Crisps: £1.25 (rounds to £1)
  • Melon: £2.75 (rounds to £3)
• Add the approximate costs of all items together: £4 + £1 + £3 = £8.
• Subtract this total from £20 to find the change: £20 - £8 = £12.
• So, Joe will receive approximately £12 in change, not £10.