There are 40 children in a classroom and n of them do not wear spectacles. (4)/(5) of the boys and (2)/(3) of the girls wear spectacles. Express the number of boys who wear spectacles in terms of n.

9514 1404 393

  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

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.

answer: get more recipes with 3 magazines for $20! i often use chicken broth instead of water. 3 tablespoons butter, divided; 1/2 cup freshly grated parmigiano-reggiano bring water and salt to a boil in a large saucepan; pour polenta slowly into 5 minutes to thicken; stir and taste for salt before transferring to a serving bowl.