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4x21 using doubling twice strategy

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4x21 using doubling twice strategy

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Answer to a math question 4x21 using doubling twice strategy

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1. First doubling:

4 \times 21 = (2 \times 21) \times 2

2. Simplify inside the parentheses:

2 \times 21 = 42

3. Second doubling:

42 \times 2 = 84

Answer:

4 \times 21 = 84

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