Pre Algebra homework help



Equivalent fractions and reducing fractions

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Problem:
Find the missing numerator or denominator:
(a) 3⁄5 = ?⁄30
(b) 2⁄3 = 22⁄?

Solution:
(a) Comapre the denominators on the two given fractions: 5 x 6 = 30
Do the same with the given numerator
⇒ Missing numerator is 3 x 6 = 18

To do that in a single step,
Missing numerator = (3⁄5) x  30 = 18
Or  3 x 30⁄5 = 18
Or  3 x  30 ÷ 5 = 18

(b) The numerators are given: 2 x 11 = 22
Do the same with the given denominator
⇒ Missing denominator is 3 x 11 = 33

To do that in a single step,
Missing denominator = 22 x  (3⁄2) = 33
Or  22 x  3⁄2 = 33
Or  22 x  3 ÷ 2 = 33

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Problem:
Reduce the following fractions to their lowest terms:
(a) 30⁄45
(b) 32⁄40
(c) 18⁄21
(d) 10⁄33

Solution:
(a) 30⁄45
Find a number (except 1) that can divide into both 30 and 45
5 is such a number
∴   30⁄45   =   30÷ 5⁄45÷ 5   =   6⁄9
Find a number (except 1) that can divide into both 6 and 9
3 is the only such number
∴   6⁄9   =   6÷ 3⁄9÷ 3   =   2⁄3
There is no number (except 1) that can divide into both 2 and 3 and therefore,
30⁄45 reduced to its lowest term is 2⁄3

Note: If you could figure out that 15 can divide into 30 and 45 both, you would need one less step:
30⁄45   =   30÷ 15⁄45÷ 15   =   2⁄3

Lesson: Try to find as large a number as you can to divide

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