B = 1 - 3/2×10 - 3/4×15 - 3/6×20 - ... - 3/198×500
B = 1 - (3/2×10 + 3/4×15 + 3/6×20 + ... + 3/198×500)
B = 1 - 3/2×5 × (1/1×2 + 1/2×3 + 1/3×4 + ... + 1/99×100)
B = 1 - 3/10 × (1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/99 - 1/100)
B = 1 - 3/10 × (1 - 1/100)
B = 1 - 3/10 × 99/100
B = 1 - 297/1000
B = 703/1000