7C Math: Fraction Problem Solving

Online math lesson:  Do the work in notebook since it is difficult to write fractions on computer.
- if these questions are too hard, I will post some easier questions, still involve fractions,  by the end of the week

I am sharing some of my original fraction problem solving based questions with you.  Try to get the common denominator first .  Will post answers in a few days.  Show all steps and calculations

Example

In a forest, 2/9 of the trees are Maple, 3/7 are Oak, ¼ are Pine and the rest are Ash trees.  If there are 128 Pine in the forest, how many Ash trees are there?

Step 1: common denominator for 9, 7 and 4 (denominators for all the fractions) is

 9 x 7 x 4 = 252

Step 2: find the equivalent fraction for each

(multiply 4x7 = 28 to the numerator and denominator) 2/9 = 2x28 = 56; 9x28 = 252

thus, 2/9 = 56/252

Step 3: or you can also use cross multiplication to find the equivalent fraction

3/7 = A/252

A = 3 x 252 ÷ 7 = 108

1/4 = B/252

B = 252 x 1 ÷ 4 = 63

Step 4: the three fractions are 56/252 (Maple), 108/252 (Oak) and 63/252 (Pine)

Step 5: Ash tree = the rest.  

1 - 56/252 - 108/252 - 63/252

= 252/252 - - 56/252 - 108/252 - 63/252

= 25/252

Step 6: 128 pines = 64/252; ash tree = 25/252

- use cross multiplication and determine that there are 50 Ash trees in the forest