Video Transcript
Use the drawn number line to
complete negative three-tenths plus what equals two-fifths.
The number line is divided into
equal intervals at every tick mark. We can find the interval between
ticks by looking at the first interval after zero. The value on the first tick after
zero is one-tenth, so the distance between each tick on this number line is
one-tenth. Therefore, for every tick we move
right on the number line, we add one-tenth, and for every tick we move left on the
number line, we subtract one-tenth. So, to get from zero to negative
three-tenths, we move three ticks to the left along the number line as shown. Counting the number of ticks to
move from negative three-tenths to two-fifths, this is seven ticks.
Multiplying the interval size of
one-tenth by the number of ticks, seven, gives us the distance, 𝑥, from negative
three-tenths to two-fifths, which is seven-tenths. Therefore, negative three-tenths
plus seven-tenths equals two-fifths. So the blank is seven-tenths.
