Question

It takes Zina 1 hours to build a model skyscraper and Rachel 3 hours to do the

same job. It will take hours to build a model skyscraper working
together?

Answer 1

It takes them 45 minutes

Explanation:

Let's say that x is the amount of work in one hour that zina does

so the amount of work that rachel does in the same hour is 1/3x, because 3 times slower

so we have

x+1/3x=100%

what does that mean?

it means the amount of hours taken to complete a skycraper

so we solve for x

x=75%

so we need to figure out how much hours does zina takes to complete 75% of the skycraper

1 hour ----- 100%

x hours ---- 75%

1 hour *75%/100%=x hours

1 hour (3/4)=x hours

60 minutes (3/4)= x minutes

x=45 minutes

Answer 2

(ignore this answer, i cant delete it srry..)