thank u but how did he get 80 ?

(Refer to model) Initially he had 5 blocks of blue pens and 1 block of red pens. After giving away a certain amount of red pens he had 1 unit worth of red pens and 7 units worth of blue pens. If u see the model, each block is equivalent to 7 units. So there’s a total of 42 units, and from there u can find 1 unit, which is basically the number of red pens he had left

If ure wondering how I got 5 blocks and 1 block, it’s because the question said that 1/6 of the pens are blue and 5/6 are red. Same concept used for the units :). 1/8 of the pens remaining are red and 7/8 of are blue.

The shaded area represents the number of pens that he sold

hi nicholas ! could u pls answer my recent question . please , it would help me . thanks