Question

What is the sum of the numbers from 1 to 70? 1 + 2 + 3 + ………. + 80 = 3240 71 + 72 + ……….. + 80 = 755

Answer 1

Step-by-step explanation:

The sum of number from 1 to 70=2485

sn=n/2{2a+(n-1)d}

=35(2+69)

=2485

Answer 2

The sum of the numbers from 1 to 70 is 2485.

GIVEN: 1 + 2 + 3 + ………. + 80 = 3240

             71 + 72 + ……….. + 80 = 755
TO FIND: Sum of the numbers from 1 to 70.

                 1 + 2 + 3 + ………. + 70 = ?
SOLUTION:

As we are given in the question,

Let this be Equation 1,

1 + 2 + 3 + ………. + 80 = 3240                         -----Eq 1

Let the other one be Equation 2,

71 + 72 + ……….. + 80 = 755                             -----Eq 2

Now,

1 + 2 + 3 + ………. + 70 = (1 + 2 + 3 + ………. + 80) - (71 + 72 + ……….. + 80 )

Now, Subtracting equation (1) & (2) .

= (1 + 2 + 3 + ………. + 80) - (71 + 72 + ……….. + 80 )

= 3240 -  755

= 2485

Therefore,

1 + 2 + 3 + ………. + 70 = 2485.

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