Mental Math Series - Part 1 Tricks

Vocabulary flashcards summarizing mental math rules, special multiplication tricks, and practice examples from the Chapter 1-5 lecture.

Two-digit multiplication by 11 (without carry)

A mental math shortcut where the outer digits of the product are the original two digits, and the middle digit is their sum (e.g., $36 \times 11 = 396$).

Two-digit multiplication by 11 (with carry)

A mental math technique used when the sum of the digits is $10$ or greater; the units digit of the sum is placed in the center, and $1$ is carried over to the first digit (e.g., $37 \times 11 = 407$).

Three-digit multiplication by 11

A mental math method where the answer starts with the first digit, followed by the sum of the first and second digits, the sum of the second and third digits, and ends with the last digit, adjusting for any carries (e.g., $423 \times 11 = 4653$).

Squaring two-digit numbers ending in 5

A mental math shortcut where the tens digit $n$ is multiplied by its consecutive integer $n + 1$, and $25$ is appended to the end of the product (e.g., $75 \times 75 = 5625$).

Multiplication of numbers with identical starting digits and unit digits summing to 10

A mental math shortcut where the shared tens digit $n$ is multiplied by $n + 1$ to form the first part of the product, and the two unit digits are multiplied together to form the final two digits (e.g., $34 \times 36 = 1224$).

$$473 \times 11$$

A three-digit multiplication example involving carries where $4 + 7 = 11$ and $7 + 3 = 10$, resulting in a final answer of $5203$.

$$95 \times 95$$

The largest two-digit squaring problem ending in 5, calculated as $9 \times 10 = 90$ followed by $25$, yielding $9025$.

$$57 \times 53$$

A multiplication problem solved using the special rule for matching tens digits and unit digits adding to 10, calculated as $5 \times 6 = 30$ and $7 \times 3 = 21$, giving $3021$.

Math Blob Run

A free mental math practice game where players save a good blob from a bad blob by quickly solving math questions.