设这个数为x.
4/5x + 24 = 120 × 1/5
4/5x + 24 = 24
4/5x = 24 - 24
4/5x = 0
x = 0
答：这个数是0.
算数方法：(120 × 1/5 - 24) ÷ 4/5
= (24 - 24) ÷ 4/5
= 0
答：这个数是0.