Arithmetic operations

1. Add all the elements of the array with the sum method. Go back to array_1:

array_1
array([[ 1,  2],
       [ 3,  4],
       [ 5,  6],
       [ 7,  8],
       [ 9, 10]])
array_1.sum()
55

1. Find all the sums by row:

array_1.sum(axis = 1)
array([ 3,  7, 11, 15, 19])

1. Find all the sums by column:

array_1.sum(axis = 0)
array([25, 30])

1. Find the mean of each column in a similar way. Note that the dtype of the array of averages is np.float:

array_1.mean(axis = 0)
array([ 5.,  6.])