Direct Proportion
As one values increases, so does the other.
Unitary method : Find the value of 1 unit,
Multiply to find the required units.
Example .
4 books cost £ 1.28. How much do 7 books cost ?
By the Rule of Three
Indirect Proportion
As one values
increases, the other decreases.
Example .
If
it takes 4 days for 10 men to dig a trench,
how
long will it take 8 men ?
By the Rule of Three
Since this is indirect proportion,
the inverse applies.