ACT · Math · Integrating Essential Skills
Matemáticas de base en problemas de varios pasos: porcentajes, proporciones, ritmos, unidades, áreas y perímetros.
Porcentajes, proporciones, ritmos, unidades y áreas en problemas de varios pasos.
\$250 → \$210: $40\div250=16$ % de bajada.
Intenta responder antes de abrir la solución. Las preguntas están en el idioma del examen.
In a club of 36 students, the ratio of boys to girls is $5:4$. How many girls are in the club?
Respuesta correcta: A. $16$
The ratio has $5+4=9$ parts, so each part is $36\div9=4$ students. Girls: $4(4)=16$.
$20$ is the number of boys. $28.8$ and $45$ multiply 36 by $\frac45$ or $\frac54$, as if 36 were the number of boys or of girls; but 36 is the whole club, which has 9 parts.
The price of a bicycle decreased from $250 to $210. By what percent did the price decrease?
Respuesta correcta: A. $16\%$
Percent change $=\frac{\text{change}}{\text{original}}\times 100=\frac{40}{250}\times 100=16\%$.
19% (about $40\div210$) divides by the new price instead of the original. 40% confuses the dollar change with a percent. 84% $(210\div250)$ is the new price as a percent of the old one, not the decrease.
A printer prints 18 pages per minute. At this rate, how many hours will it take the printer to print 3,240 pages?
Respuesta correcta: B. $3$
Time = $3{,}240\div18=180$ minutes. Convert to hours: $180\div60=3$ hours.
180 is the time in minutes, not hours. 18 is the printing rate itself. 1.8 divides 180 by 100 instead of by 60.