Explanation:
common multiples are numbers that can be divided without remainder by both numbers.
12. 3 and 5
3 and 5 are both prime numbers, so their common multiple are multiples of their product (3×5 = 15).
so,
1×15 = 15
2×15 = 30
3×15 = 45
13. 4 and 6
the prime factors of 4 are
2×2
the prime factors of 6 are
2×3
the last common multiple is the product of the longest chains of prime factors of the numbers :
2×2 × 3 = 12
6 has only one 2 factor, 4 has two 2 factors, so that is the longest chain. and 6 has one 3 factor, which makes it the longest chain for that.
the multiples for 4 and 6 and now the multiples of 12 :
1×12 = 12
2×12 = 24
3×12 = 36
4×12 = 48
14. 3 and 7
they are both again prime numbers, so we are looking for multiples of their product (3×7 = 21).
1×21 = 21
2×21 = 42
15.
what do we need to do to change the denominator by keep the overall value of the fraction ?
we need to multiply numerator and denominator by the same value (e.g. by 2/2, 3/3, 4/4, ...)
3/4 = 6/8 = 9/12 = 12/16
16.
as before.
2/3 = 4/6 = 6/9 = 8/12
17.
as before
4/5 = 8/10 = 12/15 = 16/20
18.
now we need to find the largest n/n factor hidden in the fraction. by eliminating that we get the core (simplified) value of the fraction.
4/12 = 1/3 × 4/4
so,
1/3 is the simplified fraction.
19.
as before
6/10 = 3/5 × 2/2
3/5 is the simplified fraction.
20.
as before
4/8 = 1/2 × 4/4
1/2 is the simplified fraction.