How is using mental math to add with decimals like using mental math to add whole numbers

Well, they are the same kind of because if you say 20.4+7.3 lets round it 20.4 would round to 20 and 7.3 would round to 7 so 20+7=27.

Rounding whole numbers would be 25+ 62, 25 would round to 30 and 62 would round to 60, so 30+60= 90  Exact 25+62= 87, which is really close. :) They are really the same because you are just rounding and you can round by tenths while you can't for whole number. Whole number are much easier.

Hope I helped :-)

interdependence is when all participating groups and individuals depend on each other. if you depend on one anothers goods, you end up trading in order to get the items you're looking for. (for ex: if i have food and you have water, we trade in order to depend on each other to live)