The fortieth odd number is
81
39
79
41
and the sum of the first forty odd numbers is
80
1600
158
6241

1) Third Option is correct.

2)  Second Option is correct.

Step-by-step explanation:

Since we have given that

odd numbers are as follows:

1, 3, 5, .........................

so, first term = a = 1

d = common difference = 3-1=2

n =  number of terms = 40

As we know that it forms an "Arithmetic Progression ":

so, the fortieth odd number is 79.

Hence, Third Option is correct.

Now, we need to find the first forty odd numbers :

As we know the formula :

Hence, Second Option is correct.  

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.

vertical=18cm horizontal=18cm hypotenuse=25.5

step-by-step explanation: