Question

Fourth proportion of 1/3,2/5and8.4 ​

Answer 1

1/3 : 2/5 :: 8/4 : ? let the fourth no. be = x

Product of means = Product of extremes

$\implies$1/3 * x = 2/5 * 8/4

$\longrightarrow$ ( 1+3x) / 3 = (8+40)/20

$\longrightarrow$3x +1 = 3* 48/20

$\longrightarrow$3x + 1 = 144/20

$\longrightarrow$3x = 1 + 144/20

$\longrightarrow$3x = 164 /20

$\longrightarrow$3x = 41/5

$\implies$X = 41/15