Man-su, Tae-min and Woo-jin had 210kg of kimchi altogether. Man-su gave 1/10 of his kimchi to Tae-min and 2/5 of his kimchi to Woo-jin. After that, all three guys had the same amount of kimchi. How much more kimchi did Tae-min have than Woo-jin at first?

Work Backwards / Total Unchanged:

210 / 3 = 70kg (per person in the end)

In all, Man-su gave (1/10 + 2/5) of his kimchi to Tae-min and Woo-jin:

1/10 + 4/10 = 5/10 = ½ of his kimchi

He has 1 - ½ = ½ of his of kimchi left.

Man-su has 70 x 2 = 140kg of kimchi at first.

2/5 of Man-su’s kimchi = 2/5 x 140 = 56kg (given to Woo-jin)

1/10 of Man-su’s kimchi = 1/10 x 140 = 14kg (given to Tae-min)

At first, Tae-min has 70 – 14 = 56kg of kimchi, and Woo-jin has 70 – 56 = 14kg of kimchi.

Difference between Tae-min and Woo-jin at first = 56 – 14 = 42kg of kimchi (Ans)