A swimmer has a currently won 11 out of 17 races. How many races do they need to win in order to have a winning ratio of 70%?

Question

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Answer 1

70% of 17=0.7×17=11.9 or about 12 races. 12/17=70.59%.

Answer 2

Let x be the number of races he have to win for his winning ratio to be 70% or 0.7

so,

(11+x)/(17+x)= 0.7

=> 11 +x = 0.7(17+x)

=> 11 +x = 11.9 +0.7x

=> x - 0.7x = 11.9 -11

=> 0.3x = 0.9

=> x = 0.9/0.3

=> x =3

So he have to win 3 more races. Or (11+3) = 14 races out of (17+3) = 20 races.