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(**) Multiplying Two
Numbers Whose One’s Digits Are The Same And Whose Ten’s Digits Add To 10:
A.
From algebra we learn:
(10a + b) (10(10
– a) + b) = 100((a)(10 – a) + b) + b2
B.
Using numbers instead of variables we get the following rules:
1.
Square the one’s digit. Write
this number down (make sure the number takes up 2 place values).
2.
Multiply the ten’s digits together and add to the one’s digit.
Write the result.
Ex [1] 33 x 73 =_________.
a)
32 = 9. Write 09
to take up 2 places.
b)
3 x 7 + 3 = 24. Write 24.
c)
The answer is 2409.
Ex [2] 49 x 69 =_________.
a)
92 = 81. Write
81.
b)
4 x 6 + 9 = 33. Write 33.
c)
The answer is 3381.
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