How many members in a Swim Club? 30:70

Thirty percent of the members of a swim club have passed the lifesaving test. Among the member who have NOT passed the test, 12 have taken the preparatory course and the 30 have not have not taken the course. How many members are there in the swim club?

Now I did this and came up with 60 members. 70% of the club members = 42 ...so I wanted to find out 30% of 42 to get how many people have passed which I came up with 3:7 * 42 = 18...then add the totals 18+42= 60. But that doesn't seem right. 70% of 60 does not equal 42. Please help. Am I doing this right?

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Originally Posted by thecapaccino

Thirty percent of the members of a swim club have passed the lifesaving test. Among the member who have NOT passed the test, 12 have taken the preparatory course and the 30 have not have not taken the course. How many members are there in the swim club?

Now I did this and came up with 60 members. 70% of the club members = 42 ...so I wanted to find out 30% of 42 to get how many people have passed which I came up with 3:7 * 42 = 18...then add the totals 18+42= 60. But that doesn't seem right. 70% of 60 does not equal 42. Please help. Am I doing this right?

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you are correct, and 70% of 60 is 42.

i would not really use ratios here, i'd use percentages.

now recall that "percentage" is just a fancy word for "over 100" or "/100" So 17% is the same as 17/100 and 23% is the same as 23/100 etc.

in math, "of" means multiply. so 23% of 82 means 23/100 * 82

now let's move on to the problem.

we know 42 members did not pass the test, and that this was 70% of the members. so we have 42 = 70% of the members, let x be the number of members the swim club has, so we get

42 = 70/100 * x
=> 4200 = 70x
=> 4200/70 = x
=> x = 60

Sometimes you know things but now how to explain them.

Thank you for your help. I understood things very clearly.

Cheers