Solve a proportion a : b = c : x for the missing value. Leave the unknown field empty and the calculator fills it in using cross-multiplication: x = b·c / a.
Proportions appear everywhere: converting recipe servings, scaling drawings, currency conversion at a known rate, and map distances. Any two equal ratios form one.
Frequently asked questions
How do I solve 3:4 = 9:x?
Cross-multiply: 3x = 36, so x = 12.
Which field do I leave empty?
The one you want to find — usually x, the fourth term.
What if I leave two fields empty?
The proportion cannot be solved with two unknowns; fill in exactly three values.
中文说明
解比例式 a : b = c : x，求未知项。把未知项留空，计算器会用交叉相乘 x = b·c ÷ a 自动补全。
比例无处不在：换算食谱份数、缩放图纸、按已知汇率换货币、地图测距——任何两个相等的比都构成比例。
常见问题
3:4 = 9:x 怎么解？
交叉相乘得 3x = 36，所以 x = 12。
该把哪个字段留空？
把要求的那一项留空——通常是第四项 x。
留空两个字段会怎样？
两个未知数无法求解，请恰好填入三个值。