There are 7 rocks altogether they weigh 5kg. 6 of the rocks each weigh 720g what is the weight of the other rock

680g

Step-by-step explanation:

Weight of the other rock

= 5kg - 6(720g)

= 5000g - 4320g

= 680g

680 g

Step-by-step explanation:

7 rocks ⇒ 5 kg ⇒ 5000g

6 of the rocks each weigh 720g .

So,

The total weight of those 6 rocks is,

6 rocks ⇒ 720 g × 6

             ⇒ 4320 g

Now you have to find the weight of the other rock.

There fore, let the weight of the other rock be x

x + 4320 = 5000

x = 5000 - 4320

x =  680 g

So, the weight of the other rock is 680 g.

Hope this helps you.

reduce the friction between its moving parts

step-by-step explanation:

in fact, by reducing the friction between the moving parts of the machine, it is possible to reduce the energy wasted due to this friction; therefore, more input energy is converted into useful work, and this will improve the efficiency of the machine.