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It is probably impossible to enumerate all the methods.
Apart from long multiplication you can have
Two-way partitioning:
(10 + 9) * (20 + 1) = 200 + 10 + 180 + 9 = 399
This is usually done in a 2x2 grid.
Partitioning 21
19*(20 + 1) = 19*2*10 + 19*1 = 38*10 + 19 = 380 + 19 = 399
Partitioning 19
(20 - 1)*21 = 2*10*21 - 1*21 = 42*10 - 21 = 420 - 21 = 399
Or. if you are savvy enough,
Difference of two squares
(20 - 1)*(20 + 1) = 202 - 11 = 400 - 1 = 399
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∙ 11y ago
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How do you solve -2 equals x - 19?
-21
Find two consecutive odd numbers whose product is 399?
If one of the numbers is x, then the other number is x + 2. So, x(x + 2) = 399 x^2 + 2x = 399 Complete the square by adding 1 at both sides ; x^2 + 2x + 1 = 399 + 1 Use the formula: (a + b)^2 = a^2 + 2ab + b^2 (x + 1)^2 = 400 x + 1 = (+ & - )(square root of 400) subtract 1 to both sides x = -1 (+ & -) 20 x = -1 + 20 or x = -1 - 20 x = 19 or x = -21 So, x + 2 = 19 + 2 = 21 or x + 2 = - 21 + 2 = - 19 Thus the numbers are: 19 and 21 or -19 and - 21 Check: (19)(21) = 399 (-19)(-21) = 399
What adds to 21 and multiplies to 38?
19 + 2 = 21 19 x 2 = 38
What is the prime factorization of 18 and 21?
18 = 2 x 3 x 5 x 19 21 = 3 x 7
whats 9+10?
19
How many square feet are in 21 x 19 room?
21 feet times 19 feet = 399 square feet
What minus what equals 19?
for all x; (x + 19) - x = 19
What is the sum of angles in a 21 sided polygon?
sum_of_interior_angles = (number_of_sides - 2) x 180° → if number_of_sides is 21: sum = (21 - 2) x 180° = 19 x 180° = 3420°
How do you find the least common multiple of 21 33 and 57?
Factor them. 3 x 7 = 21 3 x 11 = 33 3 x 19 = 57 Multiply the highest amount of each factor. 3 x 7 x 11 x 19 = 4389
What is the prime factorization of the number 399?
399 = 3 * 7 * 19
What is the answer for this problem 4-2-x-8x plus 19?
can't answer without some kind of an "=" in it. If you mean 4-2-x-8x+19 = 0, then it would simplify to: -9x = 21 and therefore x = -21/9 ==> x = -2 1/3
All factor pairs of 21?
1 x 21, 3 x 7, 7 x 3, 21 x 1
