Indian Mental Math: Two-Digit Multiplication Calculator

Multiply two two-digit numbers with different tens digits using the Indian rounding method: round one factor to a clean ten, then adjust by the difference. Shows every step.

Input

An Indian mental math method for multiplying two two-digit numbers with different tens digits: round one factor to a clean ten, then correct with the difference.

First number

Second number (rounded to a ten)

Enter two whole numbers from 10 to 99. Pairs with the same tens digit are outside this method.

Result

Product of 47 × 68

3,196

Rounded product

3,290

−

Correction

Product

3,196

Rounded ten

Rounded product

3,290

Correction size

Step by step

Round one factor to a ten

Add 2 to 68 to make 70. You will subtract this amount later to correct.

Multiply by the clean ten

47 × 70 = 3,290. Because it is a multiple of ten, you can do this by shifting a digit.

Find the correction

47 × 2 = 94. This is the correction for the amount you moved.

Apply the correction

3,290 − 94 = 3,196. This is the product.

Calculation breakdown

Item	Value
Rounded ten	70
47 × 70	3,290
Correction 47 × 2	94
Final product	3,196

Check: a plain multiplication also gives 47 × 68 = 3,196.

Idea: a × b equals a times the rounded ten minus a times the amount moved. The subtraction becomes addition when you round the factor down.

How it works

Round one factor to the nearest multiple of ten and record how much you moved it.
Multiply that clean ten by the other factor; this product is easy to do in your head.
Multiply the amount you moved by the other factor to get the correction.
Subtract the correction from the rounded product, or add it if you rounded up, to get the final product.
A plain multiplication is shown so you can verify the answer.

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