SME
Grade 5 Math · Problem type
Multiply decimals and whole numbers
Use this for “A notebook costs $1.65. How much do 14 notebooks cost?”
Diagram
0, 2.5, 5, 7.5, 10
Decimal: 2.5
Whole number: 4
Product: 10
This is an example. Type your own values to start a new problem.
Decimal
×
Whole number
=
Product
Formulas
2.5 × 4 = 10
Decimal × whole number = product
Assumptions
•
Multiply as if both were whole numbers. Then put the point back.
•
The product has as many places after the point as the decimal, before any end zeros are dropped.
•
Decimals to 9.99, whole numbers to 20.
Step-by-step
WE KNOW
Decimal: 2.5
Whole number: 4
FIND
product
Step 1 · Find product
2.5 × 4 = ?
Decimal × whole number = product
Write the decimal in tenths or hundredths. Multiply those, then write the decimal.
2.5 = 25 tenths
25 tenths × 4 = 100 tenths = 10
Product = 10
Check
Put the numbers back in. Both sides should match.
2.5 × 4 = 10 ✓
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Add, subtract, multiply and divide decimals
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Divide decimals by whole numbers
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Related lessons
Add, subtract, multiply and divide decimals
Main lesson
Divide decimals by whole numbers
Use this for 7.2 ÷ 4: a decimal shared into equal parts.
Subtract decimals
Use this for “Subtract: 5.27 − 2.85 = ___.”
Multiply a decimal by a decimal
Use this for “What is 0.6 × 0.3?” with tenths times tenths.
Divide by a decimal
Use this for “How many 0.5s are in 3?” (3 ÷ 0.5), or 0.24 ÷ 0.08.
Estimate sums of decimals
Use this for “About how much is 12.65 + 8.3?” by rounding each to the nearest whole number.
Estimate differences of decimals
Use this for “About how much is 12.65 − 8.3?” by rounding each to the nearest whole number.
Estimate products of decimals
Use this for “About how much is 4.8 × 6.2?” by rounding each to the nearest whole number.