umm wat woodrow meant was..
for example we'll do your qeuestion
9.6 -2.6 +4.2
we multiply each number by 10,
so its 9.6(10) -2.6(10) + 4.2(10)
that way we get 96 -26 + 42
which can be easily evaluated to 112,
but notice we multiplied each term by 10, in order to get the correct answer, we need to divide the final result (112) by 10, so we get 11.2
basically the idea is, we multiplied the set of numbers below by 10
10 (9.6 -2.6 +4.2)
to maintain equality, we hav to divide it by 10 as well so we get
[ 10 (9.6 -2.6 +4.2) ] / 10
in other words we multiplied it by one.. but multiplying the numerator by 10 helps us get rid of the decimals, do our calculation up on the numerator and then "re-divide" the reasult by 10 to maintain equality....