How much of the vegetable field does Laban then have left to grow on?

Question

Laban has acquired an allotment with a large vegetable plot. He grows lettuce on 1/3 of the vegetable land and carrots on 4/7 of the rest. How much of the vegetable field does Laban then have left to grow on?

Answer 1

The total no. of land used is = 1/3+12/7=19/21

The whole land as a whole should be 1 which is also equal to 21/21

so you take 21/21 minus the total number of land used which is 19/21

21/21-19/21=2/21

2/21 vegetable field remains.

Answer 2

1/3 = 7/21 (multiply numerator and denominator by 7)

4/7 = 12/21 (multiply numerator and denominator by 3)

1/3 + 4/7 = 7/21 + 12/21 = 19/21

The entire field is 21/21 so the amount left to grow on is 21/21 - 19/21 = 2/21