Question

How do you know when to add or subtract?

Answer 1

The lengths of XY and YZ add up to the length of XZ:

XY + YZ = XZ

We know that XZ = 10 + 1/5 = 51/5, and XY = 4 + 2/3 = 14/3, so

14/3 + YZ = 51/5

Subtract 14/3 from both sides to solve for YZ:

YZ = 51/5 - 14/3

Find a common denominator; the least common multiple of 5 and 3 is 15, so multiply the first fraction by 3/3 and the second one by 5/5 to get

YZ = 153/15 - 70/15

YZ = (153 - 70)/15

YZ = 83/15

We have 80 = 75 + 8, so that

YZ = 83/15 = (75 + 8)/15 = 75/15 + 8/15 = 5 + 8/15