Can any one EXPLAIN how to do this?

What was the difference between the highest and lowest unemployment rate amongst the group of graduates?

these are possible anwsers

10.5%

7.8%

9.3%

4.2%

3.5%

uni A in 1990, unemployed (155) employed (1475)

in 2000 unemployed (125) employed (1350)

uni B in 1990 unemployed (125) employed (1610)

in 2000 unemployed (150) employed (1250)

Can any one EXPLAIN how to do this?

Both the highest and lowest rates were at B, with a high of 10.7% (150/1400) and a low of 7.2% (125/1735). 10.7-7.2=3.5%