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SAT - Math - Ratio and Proportion

The value of x and y in the table above are related so that (y-1) is directly proportional to (x+1). What is the value of b+a?

x 0 1 2
y 10 a b

The value of x and y in the table above are related so that (y-1) is directly proportional to (x 1). What is the value of b a?

Given (y-1) = k (x+1)

from first column

10-1 = k(0+1)

k = 9

from second column

a -1 = 9*(1+1) = 18

a = 19

from third column

b-1 = 9*(2+1) = 27

b = 28

a + b = 28 + 18 = 46