Question

the ratio of the sale price of a textbook to the original price is 1:3 , the original price is 81. what is the sale price.

Answer 1

ratio 1:3 can be written as 1/3

sale price / original price : 1/3 = x / 81
this is a proportion, so we cross multiply
(3)(x) = (1)(81)
3x = 81
x = 81/3
x = 27 <== sale price

and notice that 1/3 = 27/81...these are equivalent fractions because that is what proportions are, equivalent fractions

Answer 2

(1:3)

(sale price : original price)

(x:81)

81/3= 27

x = 27

your last ratio is (27:81)

hope this helps