Question 1206526
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I'll focus on problem 1 only.


Note how 20 is the midpoint of 17 and 23.
midpoint = (a+b)/2


17 x 23 = (20 - 3) x (20 + 3)
17 x 23 = 20^2 - 3^2
17 x 23 = 400 - 9
17 x 23 = 391
I used the difference of squares rule.
The other two problems will use a similar approach.
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