The denominators are 10 and 7. So the LCD is 70
We need to change both fractions so that that both
have 70 in their denominators.
The first fraction has 10 for its denominator. In
order for that denominator to become 70 it must be
multipliued by 7. But if we multiply the denominator
by 7, we also must multiply the numerator by 7 to
offset so that we don't change the value. So we have
or
The second fraction has 7 for its denominator. In order
for that denominator to become 70 it must be multiplied
by 10. But as in the first fraction, if we multiply the
denominator by 10, we also must multiply the numerator
by 10 to offset so that we don't change the value. So
we have
or
Now we can combine the two numerators over the LCD of 70
That's the answer!
Edwin
