Calcualate 40% (0.40) times 20 to get that there are 8 boys in the class. The rest must be girls, so 20 - 8 gives you 12 girls. 25% (0.25) times the 8 boys gives you that 2 of the boys wear glasses. 50% (0.5) times the 12 girls tives you that 6 girls wear glasses. Add together the 2 boys and the 6 girls that wear glasses to get that a total of 8 students wear glasses.

3 0

3 years ago

Manny can assemble a computer by himself in 50 minutes. Lucy does the same job in 45 minutes. How long will it take to assemble

jonny [76]

Manny can assemble a computer in 50 minutes. That means, in a minute Manny does $\frac{1}{50}$ job.

Lucy can assemble a computer in 45 minutes. That means, in a minute Lucy does $\frac{1}{45}$ job.

If they are working together, in a minute they will do:
$\dfrac{1}{50} + \dfrac{1}{45}$
$= \dfrac{9}{450} + \dfrac{10}{450} \text{(equalize the denominator)}$
$=\dfrac{19}{450}$
In a minute they will do $\frac{19}{450}$ job

To finish the job they will do it in $\frac{450}{19}$ minutes or about 24 minutes.

5 0

3 years ago