L4 · Money problems: addition and subtraction clinic

Learning goal

“I can solve money problems with the standard algorithm - totals, sale prices, change and amounts still needed - estimating first and writing every answer with a dollar sign and two decimal places.”

Total — the full amount when costs are added together.

Change — the money you get back when you pay more than the cost: money given - cost.

Sale price — the cost after an amount is taken off: regular price - amount saved.

Still needed — the gap between a goal and what you have: goal - amount raised so far.

Worked example

You buy a book for $12.75 and a game for $8.49, and you pay with $25.00. Step 1 (total): estimate 13 + 8 = 21. Exact: 12.75 + 8.49 = $21.24. Step 2 (change): change is money given - cost = 25.00 - 21.24 = $3.76. Step 3 (check): 21.24 + 3.76 = 25.00. The estimate (about 21, so change about 4) agrees. Say it plainly: two-step money problems are just the L1 and L2 algorithms wearing a story. Decide the ORDER from the meaning: you cannot find change before you know the total.

Check yourself — explain it

Change is found by subtracting the total from the money given because...

Paired problem — example still visible

A hat costs $14.60 and gloves cost $9.35. You pay with $30.00. Find the total and the change. -> Total $23.95; change 30.00 - 23.95 = $6.05

Faded completion — last step is yours

"Total of $7.85 + $5.49 is $13.34. Change from $20.00: 20.00 - 13.34 = ___" -> $6.66

Ready to practise?

10 scored questions with a 3-rung hint ladder. Mastery needs 8/10 plus both gate questions.

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