Collocations for ratio - noun

high, low | male/female, pupil/teacher, etc. | benefit-to-risk, power-to-weight, etc.

achieve, have
They have a high ratio of imports to exports.

improve, increase
The hospital is trying to improve its staff/patient ratio.

reduce | calculate, find, work out

improve | worsen
the worsening pupil/teacher ratio in our schools

in a/the ~
We mixed the oil and water in a ratio of one to five.

~ between
the ratio between the amount of time spent on the work and the profit produced

~ of sth to sth
the ratio of house prices to incomes

in direct ratio to sth
Their sales rose in direct ration to the amount they spent on advertising.