By what number should (-5)power -1 be multiplied so that the product may be equal ti (10)power -1 ?

Hi Bably, given (-5)^-1 * k = (10)^-1 
So k = (10)^-1 / (-5)^-1 = 1/10 * (-5)1 = - 5/10 = -1/2
Hence it is to be multiplied by -1/2 to get the required