SME
Grade 3 Math · Number & Base Ten
Round to the nearest 10 or 100
Use this for “Round 47 to the nearest ten.”
Diagram
47 is 7 past 40 and 3 before 50.
7 is 5 or more, so it rounds up to 50.
This is an example. Type your own values to start a new problem.
Number
example
Ten below
worked out (not typed)
Ten above
worked out (not typed)
Rounded
calculated
Formulas
The ten at or below 47 is 40
The ten at or below the number = ten below
40 + 10 = 50
Ten below + 10 = ten above
47 is between 40 and 50, so it rounds to 50
The nearer ten = rounded
Assumptions
•
Find the tens just below and just above the number.
•
Round to the nearer one. 5 ones or more rounds up.
•
Rounded numbers are for estimating, like checking an answer.
•
Drag the point: every number from 35 to 44 rounds to 40.
Step-by-step
WE KNOW
Number: 47
FIND
ten below, ten above, rounded
Step 1 · Find ten below
The ten at or below 47 is ?
The ten at or below the number = ten below
Keep the hundreds and tens. Make the other digits 0.
47 = 40 + 7
Ten below = 40
Step 2 · Find ten above
40 + 10 = ?
Ten below + 10 = ten above
The next ten up is 10 more.
Ten above = 50
Step 3 · Find rounded
47 is between 40 and 50, so it rounds to ?
The nearer ten = rounded
Round to the nearer ten. Halfway (5 past) or more rounds up.
From 40 to 47 is 7. From 47 to 50 is 3.
7 is 5 or more: round up to 50.
Every number from 45 to 54 rounds to 50.
Rounded = 50
Check
Put the numbers back in. Both sides should match.
The ten at or below 47 is 40 ✓
40 + 10 = 50 ✓
47 is between 40 and 50, so it rounds to 50 ✓
Topic check
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