Starting at home, jessica traveled uphill to the grocery store for 181818 minutes at just 202020 mph. she then traveled back home along the same path downhill at a speed of 606060 mph. what is her average speed for the entire trip from home to the grocery store and back?

Step-by-step explanation:

let normal speed=x

speed uphill=x-y

speed downhill=x+y

x-y=20

x+y=60

2x=80

x=40

speed uphill=20 mph

time=18 minutes=\frac{18}{60}=\frac{3}{10} hrs

distance=speed ×time=20×\frac{3}{10}=6 miles

downhill speed=60 mph

time taken=\frac{6}{60}=\frac{1}{10} hr

total time =\frac{3}{10}+\frac{1}{10}=\frac{3+1}{10}=\frac{4}{10}

total distance=6+6=12 mile

average speed=12÷\frac{4}{10}=12×\frac{10}{4}=30 mph

total time=

c.

step-by-step explanation:

0.02

step-by-step explanation:

time of 9 192 631 770 periods of the radiation corresponding to the transition between the 2 hyperfine levels of the ground state of the caesium 133 atom at 0 k (but other seconds are sometimes used in astronomy)