WHAT ARE PARTIAL SUMS???

Answer 1

It is a method of addition, without regrouping (carrying).

for instance

459
164 add
add the 400 and 100 hundreds
500
add the 50+ 60
110
add the 9+4
13
now add those
(right to left)
643
http://www.nychold.com/em-arith.html

Answer 2

grade 1 215
grade 2 186
grade 3 259
how many more were sold bt grade 3 than by grade 2? 73 answer

why aren't any of the tens regrouped to subtract the ones?