For percentage questions it is better to think in terms of numbers

so given information:

1966: mortality rate 81 ppl out of 1000
1974: mortality rate is 48 ppl out of 1000

in 1970 it has declined by 20% of 1966 level

i.e. level in 1970== 80*81/100
that gives a level of 64.8 ppl in 1000

so decrease from 70 to 74= 64.8-48=26.8

so percentage rate= (26.8/64.8)*100===41.3%



let us know the answer

approx 25%

In 1966 the operative morality rate in country was 8.1%. By 1974 it declined to 4.8% .If the rate declined by 20% from 1966 to 1970,by approximately what percentage rate declined from 1971-1974?

1966 rate is 8.1%. This rate declined by 20% from '66 to '70

Therefore rate at '70 is = 80/100 * 8.1 = 6.48%

Rate at '74 is 4.8%

Difference in rate of '70 and '74 is 6.48 - 4.8 = 1.68%

Therefore BY what percent did the rate decline?

= 1.68 / 6.48 * 100
Approx 1.7 / 6.5 * 100
= 26%

If closest answer choice is 25% pick that.