Respuesta :

mathmate
heart beats 12 times every 5 seconds, i.e. using proportions,
12/5 = x/60
Cross multiply:
x=60*12/5=144

Answer, Julie's heart beats 144 times per minute while exercising.
altavistard
Write and solve an equation of ratios, as follows:

5 sec           12 beats
---------  =    -------------
60 sec                x

5x=720       x= 144 beats in 60 sec