# Thread: Need to find formula

1. ## Need to find formula

Because tsunamis travel very quickly, warning people of an approaching tsunami can be difficult. In 1998, some mexican scientists developed a new method of measuring earthquakes and predicting tsunamis. Before 1998, it took 20 minutes to determine whether and earthquake would produce a tsunami. With the new technology te task may be completed in 5 minutes. What percentage decreases in time is this ?

Thanks, Chhoeuk

2. Originally Posted by chhoeuk
Because tsunamis travel very quickly, warning people of an approaching tsunami can be difficult. In 1998, some mexican scientists developed a new method of measuring earthquakes and predicting tsunamis. Before 1998, it took 20 minutes to determine whether and earthquake would produce a tsunami. With the new technology te task may be completed in 5 minutes. What percentage decreases in time is this ?

Thanks, Chhoeuk
Hi,

the absolute decrease of time: 15 min

Let p be the percentage you are looking for. Then use the proportion:

15/20 = p/100 ===> p = 75%

EB