その計算けいさん、間違まちがってるよ。

sono keisan, machigatteru yo.

That calculation is wrong, you know. casual

彼かれの考かんがえ方かたは間違まちがっていると思おもいます。

kare no kangaekata wa machigatte iru to omoimasu.

I think his way of thinking is mistaken. neutral