Round to One or Two Digits (Significant Figures)

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Opens on Chapter 2’s example: 4,782 to one digit, and 38 × 64 rounded two ways.

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From the book, Chapter 2. 4,782 rounds to 5,000, a move of 4.6%. A one-digit round can be off by up to 33% for a number starting with 1 but only 5% for one starting with 9. For 38 × 64, rounding both up is 15% high; one up and one down is 1.3% low. The Moon’s 238,855 miles to two digits is 240,000.

Rounding is half up, the way the book rounds. Numbers can be typed as 1,450, $38, 12%, 1/20, 2.5 million or 3 × 10⁷. Everything stays in your browser: no sign-up, nothing stored or sent.