SME
Grade 2 Science · Problem type
Slowing erosion with a wall
Use this for “With no wall the bank wore back 30 cm. With a wall it wore back 8 cm. How much did the wall help?”
Picture
30
8
Less worn back with a wall: 22 cm
This is an example. Type the numbers from your problem to start.
Bank worn back, no wall (cm)
−
Bank worn back, with a wall (cm)
=
Less worn back with a wall (cm)
Number sentences
30 − 8 = 22
Good to know
•
People build walls and plant grass to slow down erosion.
•
Measure how far each bank moved back in the same rain.
•
The difference shows how much the wall helped.
Step-by-step
WE KNOW
Bank worn back, no wall: 30 cm
Bank worn back, with a wall: 8 cm
FIND
less worn back with a wall
Step 1 · Find less worn back with a wall
30 − 8 = ?
Count up from the bank with a wall to the bank with no wall. That is how much less the bank wore back.
8 + 2 = 10
10 + 20 = 30
Jumps: 2 + 20 = 22
Less worn back with a wall: 22 cm
Check
Put the numbers back in. Both sides should match.
30 − 8 = 22 ✓
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