Probability question Please help i need to learn the method?

EvilNintendoGuy

New member
I really get stuck with ratios.
The ratios of boys to girls in a mathematics class is 4:5. The number of girls increase from 15 to 18.

what is the new ratio of of boy to girls?

what is the best way to answer this without a calculator?
Im thinking because

5/9 = 18 then 18 divided 9 which is 2 is a part
thereforce Boys equals 2*4 which is 8
Sheet that wouldn't be right because i haven't recognized that the boys number never changed.
 
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