8/7 x 9/45 x 5/8 x 9/72

Question

What is the rule for multiplying multiple fractions. ? I don't even know where to begin.

Answer 1

(8/7)(9/45)(5/8)(9/72)

simplify the fractions first if possible

(8/7)(1/5)(5/8)(1/8)

simplify again if possible by dividing a numerator and a denominator by the same number

rearrange the fractions

(8/7)(1/8)(1/5)(5/8)

(8/7)(1/8)=1/7

(1/5)(5/8)=1/8

(1/7)(1/8)=(1*1)/(7*8)=1/56

the rule is multiply all the numerators together and then multiply all the denominators together

the product of the numerators over the product of the denominators is the answer, but you then have to simplify your answer so it's easier to simplify before you multiply

suppose we did not simplify first...

the answer would be 3240/181,440

now you have to write the answer in lowest terms which is quite the task...

3240/181,440=324/18,144=81/4536=9/504=1/56 and I can recognize common factors easier than students

so the best thing to do is simplify before you multiply