Explanation:
a = original number of adult tickets
c = original number of child tickets
a/c = 2/5
a = 2c/5
(a+70)/(c+300) = 1/3
(2c/5 + 70)/(c + 300) = 1/3
2c/5 + 70 = (c + 300)/3
2c + 350 = 5(c + 300)/3
6c + 1050 = 5(c + 300) = 5c + 1500
c = 450
a = 2c/5 = 2×450/5 = 2×90 = 180
Joshua sold therefore in total
180 + 70 = 250 adult tickets.
and by the way
450 + 300 = 750 child tickets.