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40% of a class of 40 pupils were boys. Suppose 20% of the girls left and 5 boys joined the class. What is the ratio of the number of boys to the number of girls now?

Sagot :

Boys: 0.40 (40) = 16 
Girls: 40 - 16 = 24

20% of the girls left:  24 - (0.20) (24) = 24 - 4.8 = 19. 2 or 19 girls
5 boys joined the class:  16 + 5 = 21 boys

After 5 girls left, and 5 boys joined the class, the ratio of boys to girls is now
21 : 19
 

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