Python Mental Math Shortcuts for the Exam Hall

Powers of 2

Memorise up to 2^10 = 1024. Shifts appear in bitwise questions.

Modulo Shortcuts

• n % 2 — parity (0 = even).
• n % 10 — last digit.
• n // 10 — drop the last digit.

Integer Division Tricks

• n // 2 — halve (floor).
• n * 10 + d — append a digit.

Digit Sum in 2 Lines

def digit_sum(n):
    return sum(int(c) for c in str(abs(n)))

Rounding Quick Wins

• round(x, 2) — 2 decimals (banker's rounding).
• int(x) — truncate toward zero.
• math.floor(x) — toward negative infinity.