2ln10+log20/log121-ln11 equals -18.743, why and how?
$${\mathtt{2}}{\mathtt{\,\times\,}}{ln}{\left({\mathtt{10}}\right)}{\mathtt{\,\small\textbf+\,}}{\frac{{log}_{10}\left({\mathtt{20}}\right)}{{log}_{10}\left({\mathtt{121}}\right)}}{\mathtt{\,-\,}}{ln}{\left({\mathtt{11}}\right)} = {\mathtt{2.831\: \!933\: \!610\: \!243\: \!228\: \!5}}$$
It is because division is done before addition and subtraction Remember PEDMAS 
To do it on the calc you need to put more brackets in, then it gives you the answer that you seek :))
( 2ln10+log20 ) / ( log121-ln11 )
$${\frac{\left({\mathtt{2}}{\mathtt{\,\times\,}}{ln}{\left({\mathtt{10}}\right)}{\mathtt{\,\small\textbf+\,}}{log}_{10}\left({\mathtt{20}}\right)\right)}{\left({log}_{10}\left({\mathtt{121}}\right){\mathtt{\,-\,}}{ln}{\left({\mathtt{11}}\right)}\right)}} = -{\mathtt{18.743\: \!302\: \!368\: \!896\: \!347\: \!2}}$$
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