RAFTAAR + SPEED VERSE Calculation Shortcuts

Vocabulary-based flashcards teaching mental math shortcuts, Vedic math principles, and competitive exam calculation formulas from Mohit Goyal Sir's lecture.

Digit Sum (Beejank)

The process of summing digits of a number until a single digit is reached, where the digit $9$ is treated as $0$.

Base Method Deficit

The value calculated as $Base - Number$; used in multiplication where the left result is $N1 - \text{deficit2}$ and the right result is the product of deficits.

Complement (Nikhilam Subtraction)

A subtraction shortcut for values subtracted from powers of $10$ (like $1000$) using the pattern: All from $9$, last from $10$.

a% of b = b% of a

The percentage symmetry rule that allows flipping values to simplify mental math, such as calculating 1200\text{\}% \text{ of } 25 instead of 25\text{\}% \text{ of } 1200.

x5 Shortcut

A multiplication shortcut where a number is multiplied by $10$ and then divided by $2$ (i.e., $\frac{x \times 10}{2}$).

x25 Shortcut

A multiplication shortcut where a number is multiplied by $100$ and then divided by $4$ (i.e., $\frac{x \times 100}{4}$).

x125 Shortcut

A multiplication shortcut where a number is multiplied by $1000$ and then divided by $8$ (i.e., $\frac{x \times 1000}{8}$).

Left-to-Right Addition

A brain-friendly calculation method where you add hundreds, then tens, then units to avoid traditional carry-over confusion.

Vertically & Crosswise (2-Digit)

A multiplication pattern involving three steps: multiplying units, cross-multiplying and summing the products, and multiplying tens.

Same Tens Unit Sum 10 Trick

A shortcut for numbers like $63 \times 67$ where the tens are identical and units sum to $10$; calculated as $\text{tens} \times (\text{tens} + 1) | \text{unit} \times \text{unit}$.

Square Ending in 5 (n5^2)

A formula where the result is found by multiplying the first digit(s) $n$ by $n+1$ and appending $25$ to the end: $n(n+1)|25$.

x11 Pattern

A multiplication shortcut for a 2-digit number $ab$ that results in the digits formatted as $a | a+b | b$.

Division by 5 Shortcut

A mental math rule where you multiply the number by $2$ and divide by $10$ (i.e., $\frac{x \times 2}{10}$).

Division by 25 Shortcut

A mental math rule where you multiply the number by $4$ and divide by $100$ (i.e., $\frac{x \times 4}{100}$).

Square Root Inspection (Unit Digit Map)

A method to find roots by pairing from the right and mapping the last digit to its possible root unit digits (e.g., unit $9 \rightarrow 3$ or $7$).

Cube Root Unit Flip

The specific mapping rule for cube roots where the unit digit $2 \rightleftharpoons 8$ and $3 \rightleftharpoons 7$, while others remain unchanged.

Successive Percentage Formula

The formula used to find the net change of two consecutive percentage changes: $x+y+\frac{xy}{100}$.

CI vs SI Difference (2 Years)

The formula for the difference between Compound Interest and Simple Interest over two years: $P \times (\frac{r}{100})^2$.

CI vs SI Difference (3 Years)

The formula for the difference between Compound Interest and Simple Interest over three years: $P \times (\frac{r}{100})^2 \times (3 + \frac{r}{100})$.

Average Speed (2 Trips)

The harmonic mean formula used to calculate average speed for two trips of equal distance: $\frac{2ab}{a+b}$.

Base Method Padding Trap

A common error where the right-hand part of a base multiplication does not have the correct number of digits (e.g., must be $2$ digits for Base $100$).

DI Approximation Rule

The practice in Data Interpretation of rounding to the nearest $10$ or $100$ and keeping error below 1\text{\}% .