9514 1404 393
Answer:
b = 80 -6n . . . . boys who wear spectacles
Step-by-step explanation:
We know the ratio of boys who wear spectacles to those who don't is ...
(4/5) : (1 -4/5) = 4 : 1
If we let b represent the number of boys who wear spectacles, then the number who don't is b/4. Then total number of boys is then b +b/4 = 5b/4. The number of girls in the classroom is this number less than 40.
Let's define a few groups:
Then the total of children who do not wear spectacles is ...
n = b/4 +(1/3)(40 -5b/4)
12n = 3b +(160 -5b) = 160 -2b . . . . multiply by 12
2b = 160 -12n . . . . . . . . . . . . . add 2b-12n
b = 80 -6n . . . . the desired relation, b = boys who wear spectacles
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Additional comment
The only values of n that make sense in this context are {8, 10, 12}, corresponding to {0, 15, 30} total girls and {40, 25, 10} total boys.
