Numbers and operations

Your goal

Use place value to compare decimals, add prices accurately and explain a budget decision.

Before you begin

You should be able to add whole numbers and multiply by a small whole number.

1. Read each place

In 23.45, the digits represent 20 + 3 + 0.4 + 0.05. A zero at the end does not change the value: 0.8 = 0.80. Align decimal points so you compare or add the same units.

2. Add prices, one step at a time

1. Write 125.50 + 74.50 with the decimal points aligned.
2. Add the fractional parts: 0.50 + 0.50 = 1.00.
3. Add the whole parts: 125 + 74 = 199.
4. Combine them: 199 + 1 = 200 HTG. From 250 HTG, the change is 250 − 200 = 50 HTG.
5. Estimate to check: about 126 + 75 = 201, close to the exact total of 200.

3. Compare without guessing

Compare 0.8 and 0.75 by writing 0.80 and 0.75. Eight tenths is larger than seven tenths. Counting decimal digits would give the wrong reasoning.

Try independently

Three notebooks cost 42.50 HTG each. Is a budget of 125 HTG enough? Calculate the shortfall or change.

Which is larger: 2.09 or 2.9? Explain using place value.

Calculate 18.75 + 6.50. Check your answer with an estimate.

Keep these habits

• Align places, not the rightmost digits.
• Write units with money and measurements.
• Estimate first; use exact values for the final budget decision.