In a school 50% of the students are younger than 10, 1/20 are 10 years old and 1/10 are older than 10 but younger than 12, the remaining 70 students are 12 years or older. How many students are 10 years old?
less than 10 ---- .50
10 yrs old ----- .20
10 < n < 12 , why not say they are 11
11 yrs old ---- .10
so far we have 80%, so 20% are 12 and older
.2 n = 70
n = 350
since 10 years old make up 20%, there are 70 ten year olds
check:
< 10 = .5(350) = 175
age 10 = .2(350) =70
age 11 = .1(350) = 35
so far we have 175+70+35 = 280, leaving us with 350-280 = 70
so my answer is correct