OK, so you have 40 boys and 30 girls. That’s easy enough to calculate because you’re given a part:whole ratio (boys to total students) and you already know the total number of students is 70.

Be careful about the second ratio, though, because it’s a part:part ratio! If the ratio of older to younger is 2:3, then the ratio of older to ALL STUDENTS is 2:5. (To figure this out, imagine that you only have 2 older kids and 3 younger kids). So you have 2/5*70 = 28 kids 10 or older, and 70 – 28 = 42 kids younger than 10.

To finally answer the question, we know 2/3 of the girls, or 20 girls, are less than 10. That means the other 42 – 20 = 22 kids younger than 10 must be boys.

If there are 40 boys, and 22 of them are younger than 10, then the other 18 must be 10 or older.

from Tumblr https://ift.tt/2ZtrNwv

## Leave a Comment