Multiplication Tricks
Sum of tens digit is 10 and remaining digits are same.
Let 3n and 7n are the numbers where n is an integer and 0 ≤ n ≤ 9.
STEP 1:First we have to check,sum of tens digit is 10 and remaining digits are same.
STEP 2:$ (3 \times 7 + n)$ which gives the left hand side answer.
STEP 3: Multiply unit digit of the given number which gives the right hand side answer. It has to take up 2 digit.
Combing the STEP 1 output and STEP 2 output we will get the final result.
In General,
$(3n) \times (7n)= \underparen { \quad \text{10's digit of 1st no.} \times \text{10's digit of 2nd no.} + n \\ \text{LHS ANSWER}}$ $ \qquad \underparen {\qquad n\times n \\ \text{RHS ANSWER}}$
Example 1: Find $92 \times 12 $?
STEP 1: $ 2 \times 2 = 04 $ [RHS ANSWER]
STEP 2: Here n=2, $9 \times 1 + 2 =11$ [LHS ANSWER]
STEP 3: Combining the STEP 1 and STEP 2 together we will get our final result i.e 1104
Example 2: Find $82 \times 22 $?
STEP 1: $ 2 \times 2 = 04 $ [RHS ANSWER]
STEP 2: Here n=2, $8 \times 2 + 2 =18$ [LHS ANSWER]
STEP 3: Combining the STEP 1 and STEP 2 together we will get our final result i.e 1804
Example 2: Find $37 \times 77 $?
STEP 1: $ 7 \times 7 = 49 $ [RHS ANSWER]
STEP 2: Here n=7, $3 \times 7 + 7 =288$ [LHS ANSWER]
STEP 3: Combining the STEP 1 and STEP 2 together we will get our final result i.e 2849