F. Financial Literacy · Money and Finances: Paying, Saving and Smart Choices

Estimating the Cost of Several Items

F1.2 A1About 35 minutes

Learning goals

I can round whole-dollar prices to the nearest $10 (or $5) to estimate.
I can estimate the total cost of several items in my head.
I can use an estimate to decide if I have enough money.
I can estimate the change I will get.
I can tell when an estimate is too close to call and I need the exact total.

Words to know

estimate
A close answer that you can find quickly in your head.

round
Change a number to a nearby friendly number, like $28 → $30.

total
The cost of all the items added together.

whole-dollar amount
A price with no cents, like $14 or $39.

transaction
Buying and paying for something.

reasonable
Makes sense; close to what you expected.

Remember from Grade 3

In Grade 3 you estimated change using friendly numbers, and you found the total for two or three small items. In Grade 4 you will estimate the total for several items, with prices up to about $100, all in your head.

Let's start with a story

Winter is coming! Owen and his dad go to the Winter Sports Sale with $50. Owen grabs a toque ($14), mittens ($18) and a scarf ($23).

At the end of the aisle, Dad asks, "Do we have enough money for all three?"

Owen doesn't have paper. He doesn't need it! He can estimate.

Knitted toques, mittens and scarves are stacked on a wooden table in a store. — Toques, mittens and scarves like Owen's. Rounding each price to the nearest $10 helps you estimate the total in your head. AI-generated image

Item	Price
Toque	$14
Mittens	$18
Scarf	$23
Water bottle	$9
Skating socks	$7
Ski goggles	$28
Sled	$31
Hockey stick	$39
Helmet	$46
Skates	$64

The Winter Sports Sale. Every price is in whole dollars. There is no tax in this unit.

How to estimate a total

Round each price to a friendly number. For most prices, round to the nearest $10.
Add the friendly numbers in your head.
Ask: Is my estimate close to the money I have? If it is very close, find the exact total to be sure.

Rounding to the nearest $10

Look at the ones digit.

0, 1, 2, 3 or 4: round down. $14 → $10.
5, 6, 7, 8 or 9: round up. $18 → $20. $65 → $70.

A number line shows which ten is closer.

14 is closer to 10. 18 is closer to 20. 23 is closer to 20.

Worked example

Example 1: Owen's estimate

Estimate the total for the toque $14, mittens $18 and scarf $23. Is $50 enough?

Round each price: $14 → $10, $18 → $20, $23 → $20.
Add: $10 + $20 + $20 = $50.
The estimate is exactly $50, the money they have. That is too close to call!
Find the exact total: $14 + $18 = $32. Then $32 + $23 = $55.

The estimate is about $50, but the exact total is $55. $50 is not enough. Owen puts the scarf back.

Rounding to the nearest $10 gives a quick estimate. When the estimate is very close to the money you have, find the exact total.

Too close to call

When your estimate is very close to the money you have, don't guess. Rounding down can make an estimate a little too small, and rounding up can make it a little too big. Work out the exact total.

Worked example

Example 2: Round up to be safe

Pia has $40. She wants a water bottle $9, skating socks $7 and a toque $14. Is $40 enough?

To be safe, round every price up to the next ten: $9 → $10, $7 → $10, $14 → $20.
Add: $10 + $10 + $20 = $40.
Every rounded price is more than the real price, so the real total must be less than $40.
Check: $9 + $7 + $14 = $30.

Yes, $40 is enough. The exact total is $30, so Pia will even get $10 back.

Worked example

Example 3: Round to the nearest $5

Estimate the cost of a hockey stick $39 and a helmet $46.

Nearest $10: $40 + $50 = $90.
Nearest $5 is closer: $39 → $40, $46 → $45. $40 + $45 = $85.
Exact: $39 + $46 = $85.

About $85 to $90. Rounding to the nearest $5 gave an even closer estimate.

Worked example

Example 4: Estimate the change

Ali buys a scarf $23 and mittens $18. He pays with a $50 bill. About how much change will he get?

Estimate the total: $23 → $20 and $18 → $20. $20 + $20 = $40.
Estimate the change: $50 − $40 = $10.
Exact: $23 + $18 = $41. $50 − $41 = $9.

About $10 in change. (Exactly $9.) If the cashier gave Ali $19 or $1, he would know something was wrong.

Estimate, then check

An estimate helps you before you pay (Do I have enough?) and after you pay (Does my change make sense?). Say your thinking out loud: "About $20 plus about $20 is about $40."

Just for fun

Why does $18 always get invited to parties?

Because it knows how to round up its friends!

Hands-on activity

Flyer estimate game

You need: a store flyer (or 10 sticky notes with whole-dollar prices from $5 to $70 that you make up with a grown-up), paper and a pencil.

Each player secretly picks three items and writes the prices down.
Swap lists. Each player estimates the total of the other's list in their head and says it out loud.
Now find the exact total together on paper (or a calculator).
The player whose estimate was closest gets a point. Play 5 rounds.
Bonus round: a grown-up says "You have $50." Estimate: is it enough? Then check.

Math talk: "Did you round to the nearest $10 or $5? Which gave a closer estimate?"

Your turn

Round $28 to the nearest $10.

Round $46 to the nearest $10.

Estimate the cost of a toque ($14) and mittens ($18).

Estimate the cost of a sled ($31) and a hockey stick ($39).

Estimate the cost of skates ($64) and a helmet ($46).

Is $50 enough for a scarf ($23) and ski goggles ($28)?

You buy mittens ($18) and a toque ($14) with a $50 bill. Estimate your change.

More practice: warm-up

Round $12 to the nearest $10.

Round $37 to the nearest $10.

Round $55 to the nearest $10.

Estimate $21 + $19.

Estimate $8 + $11 + $10.

More practice: on your own

Estimate the cost of a sled ($31), a scarf ($23) and a toque ($14). Is your estimate higher or lower than the exact total?

Nadia has $40. Can she buy a hockey stick ($39) and a water bottle ($9)?

Will $100 pay for skates ($64) and ski goggles ($28)?

Estimate the cost of two helmets at $46 each.

Ben says a water bottle ($9), skating socks ($7) and a toque ($14) cost about $60. Is that reasonable? Explain.

Challenge

You have $60. You want mittens $18, a scarf $23, a water bottle $9 and skating socks $7. Rounding every price up gives $70. Does that mean you can't buy them all? Find out.

Find two items from the sale whose estimated total is $50 (rounding to the nearest $10). Then find their exact total.

Lily buys skates ($64), a helmet ($46) and a hockey stick ($39). She pays with two $100 bills. Estimate her change, then find it exactly.

Check your understanding

Quiz

Round $33 to the nearest $10.

What is the best estimate for $19 + $42?

Estimate $29 + $18 + $11.

Ella has $30. A shirt costs $12 and a hat costs $17. Is $30 enough?

Why is it smart to estimate before you pay?

You pay $50 for an item that costs $21. About how much change should you get?

For parents and teachers

What your child is learning: the Ontario curriculum (F1.2) asks Grade 4 students to estimate and calculate the cost of transactions with several items priced in whole dollars, not including sales tax, and the change needed for cash payments, using mental math. This lesson focuses on estimating: rounding to the nearest $10 (or $5), adding the rounded prices, and deciding whether there is enough money. Lesson 3 does the exact calculations. Estimating and checking for reasonableness are also key mathematical processes (A1).

Common difficulties:

Rounding the wrong way, especially numbers ending in 5 ($55 → $60) or forgetting to look at the ones digit.
Trusting an estimate that is too close. If the estimate equals the money available, the exact total may be a little more or less. Teach "too close to call, so calculate."
Rounding only some prices, or adding the original and rounded numbers together.

How to help: At the store, pick three items and ask, "About how much will these cost?" before you reach the checkout. Sales tax is not part of Grade 4, so explain that real totals at the till will be a bit higher because of tax, and that's something they will learn about later.