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Lesson 3: Strategies for subtracting within 1,000

# Adding and subtracting on number line

Sal adds and subtracts numbers like 585 and 368 using a number line. Numbers used in these problems are less than 1000.

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• Can you subtract 54-65? Can you? If you can, what is the answer?
• 54-65 would create a negative number

50-60 = -10
4-5 = -1
-10 + -1 = -11
• What does 256 round to the nearest 10?
• Look at the digit just to the right of the tens digit, that is, the units digit. This digit is 6.

6 is 5 or greater, so round up. Add 1 to the tens digit. Change all digits to the right of the tens digit to 0's.

Have a blessed, wonderful day!
• Why use number lines when you can use the standard algorithm because number lines take to much time
• Number lines are a way to add and subtract number intuitively.
Of course you can use your "standard algorithm", but the number line helps people who don't understand this topic to visualize it.
• if you don't know ask me when you see me talking in the chat
(1 vote)
• what is 5600 times 8900
(1 vote)
• 5,600 × 8,900
= 56 × 100 × 89 × 100
= 56 × 89 × 100 × 100
= (50 + 6) × (80 + 9) × 10,000
= (50 × 80 + 50 × 9 + 6 × 80 + 6 × 9) × 10,000
= (5 × 10 × 8 × 10 + 5 × 10 × 9 + 6 × 8 × 10 + 54) × 10,000
= (5 × 8 × 10 × 10 + 5 × 9 × 10 + 48 × 10 + 54) × 10,000
= (40 × 100 + 45 × 10 + 480 + 54) × 10,000
= (4,000 + 450 + 534) × 10,000
= 4,984 × 10,000
= 49,840,000
(1 vote)