差 and 比率: subtraction and a relative comparison
Read a difference separately from a ratio, using simple values to show that the same difference need not give the same ratio.
A difference found by subtraction
差, read さ, means a difference. 二つの箱の重さの差は二キロです。 says that the weight difference between two boxes is two kilograms.
Three and five kilograms, and eight and ten kilograms, both differ by two kilograms. That does not make the individual weights equal across the pairs.
A ratio relative to a base
比率, read ひりつ, means a ratio comparing quantities. 三対五と八対十では比率が違います。 says that three to five and eight to ten are different ratios.
With the smaller weight as the base, the larger-to-smaller comparisons are five divided by three and ten divided by eight. Distinguish a subtraction result from a quotient relationship.
Comparison order and units
In AとBの比率は二対一です。, A represents two parts and B one. Check the order rather than reversing it to make B twice A.
Use matching units to calculate a difference, and identify the quantities and their order for a ratio. 差 and 比率 provide different information about the same comparison.
Do three and five, and eight and ten, have equal ratios because their differences match?
Show the answer and why
No. Both differences are two, but three to five differs from eight to ten. Separate an absolute difference from a relative ratio.