Sum of the decimal places = 7 .Since the last digit to the extreme right will be zero ( 5 * 4 = 20), so there will be 6 significant digits to the right of the decimal point....
Let the total length of pencil = L cm Then, black part = L/8∴ Remaining part = L - L/8 = 7L/ 8 and White part = (7L/8)/2 = 7L/8∴ Remaining part = L - (L/8 + 7L/16) = 7L/16∴ length of blue part = 7L/16According to the question, 7L/16 = 31/2⇒ 7L/16 = 7/2 ∴ L =8
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