Tricks Vault

Averages Average of Evenly Spaced Numbers Average a sequence without adding every term. Interest CI − SI for 2 Years Find the gap between compound and simple interest for 2 years instantly. Fractions Compare Fractions Fast Decide which of two fractions is larger without a common denominator. Number System Count the Factors of a Number Count all factors of a number from its prime factorisation. Number System Quick Divisibility Rules Check divisibility without doing the division. Number System Unit Digit of Large Powers Find the last digit of a huge power quickly. Fast Multiplication Multiply by 11 Instantly Multiply any two-digit number by 11 without a single multiplication. Fast Multiplication Multiply Numbers Near 100 Multiply two numbers just below 100 in seconds. Percentages Percentage ↔ Fraction Turn awkward percentages into simple fractions to calculate in your head. Percentages Successive Percentage Change Combine two percentage changes into one in a single step. Percentages x% of y = y% of x Swap the numbers in a percentage to make it easier. Profit & Loss Same Selling Price Trap Spot the guaranteed loss in the classic “same selling price” question. Squares Square a Number Ending in 5 Square any number ending in 5 instantly.