Convert the octal number 0.4051 into its equivalent decimal number.

Key idea: convert each octal fractional digit d at position n to decimal by computing d × 8⁻n, then sum.

Apply to 0.4051 (base 8):

• 4 × 8⁻1 = 4 × 1/8 = 0.5

• 0 × 8⁻2 = 0 × 1/64 = 0

• 5 × 8⁻3 = 5 × 1/512 = 0.009765625

• 1 × 8⁻4 = 1 × 1/4096 = 0.000244140625

Sum the contributions:

0.5 + 0 + 0.009765625 + 0.000244140625 = 0.510009765625

Therefore the exact decimal equivalent is 0.510009765625. Rounded to seven decimal places this is 0.5100098, which matches the given correct option.