Scientific notation represents numbers as

#color(white)("XXXX")#a mantissa multiplied by #10# to an exponent

#color(white)("XXXX")##color(white)("XXXX")#where the "mantissa" is a single non-zero digit followed by a decimal point and a sequence of remaining digits, and

#color(white)("XXXX")##color(white)("XXXX")#the exponent indicates the number of decimal digit locations the decimal point needs to be moved to the right to represent the intended value.

The mantissa for #1550# is #1.550#

The exponent, the number of places to the right we need to move the decimal point of #1.55# to the right in order to make it equivalent to #1550# is 3.