Multiply by 11 Trick

An understanding of place value and the standard algorithm for multiplication explain why the x11 “trick” works when multiplying a two-digit number by 11.

An understanding of place value and the standard algorithm can also explain the 10 groups and 1 more group method.

Remember, For a fact like 11 × 7, think 10 × 7 = 70, then add another group of 7 to make 77.

For a fact like 11 x 15, think 10 x 15 = 150, then add another group of 15 (150 + 15) to make 165.