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You can multiply by 12, 13, 14, 15, 16, 17, 18, or 19 the same way. For ease of writing, these numbers will be referred to as 1a, where a is the last digit.
1. When multiplying "n" x 1a, first multiply a by the last digit of "n". Write this number down, carry if necessary.
2. Now multiply the remaining digits by a and add back to "n". Write this result.
Ex [1] 52 x 17 =________.
a) 7 x 2 = 14 so write 4 and carry *1.
b) 7 x 5 = 35 so add 35 + 52 = 87 + *1 = 88. Write 88.
c) The answer is 884.
Ex [2] 84 x 16 =_________.
a) 6 x 4 = 24 so write 4 and carry *2.
b) 6 x 8 = 48 + *2 = 50. 50 + 84 = 134. Write 134.
c) The answer is 1344.
Ex [3] 113 x 12 =_________.
a) 2 x 3 = 6 so write 6.
b) 2 x 11 = 22. 22 + 113 = 135. Write 135.
c) The answer is 1356.
B. Sometimes, as in Ex [2], it is easier to add the carried number first, before adding back to "n".