A. Group of cross country runners decided to go on an hour and a half run. During the first hour, they ran a total of 13 kilometers. Then, they ran 5.0 kilometers during the next half an hour. What was the group's average speed for the entire run?

The average speed for the entire run is 12 km/h.

Explanation:      

The average speed is given by the following equation:

Where:

: is the total distance

: is the total time

If during the first hour, they ran a total of 13 kilometers and then, they ran 5.0 kilometers during the next half an hour we have:

Hence, the average speed is:

Therefore, the average speed for the entire run is 12 km/h.

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explanation:

v=uf/(u-f)

= 5.-10/(5+10) convex lens has negative focal length

  the grams     of oxygen gas   that can be produced     is 20.6   grams of o₂

calculation

2liclo₃ →   2 licl + 3 o₂

step 1:   find the moles of liclo₃

moles = mass÷ molar mass

from periodic table the molar mass of liclo₃ =6.9 +35.5   +(16 x3) =90.4 g/mol

moles=38.7 g÷90.4 g/mol=0.4281   moles

step 2:   use the   mole ratio   to calculate the moles of o2

from equation above, liclo₃: o₂   is 2: 3  

therefore the moles of   o₂=0.4281 moles x3/2 =0.6422   moles

step 3: find mass   of o₂

mass= moles x molar mass

from periodic table the   molar mass of   o₂ = 16 x2= 32 g/mol

mass=0.6422   moles   x   32 g/mol = 20.6 grams of o₂