A sequence of numbers which go up (or down) by a fixed amount each time is called an arithmetic progression (AP). For example, the sequence  $1^{}\text{st}$term $= 5.8$, $2^{}\text{nd}$ term $= 6.0$, $3^{}\text{rd}$ term $= 6.2$, $4^{}\text{th}$term $= 6.4$  is an AP because the terms go up by $0.2$ every time.  If the $1^{}\text{st}$ term of an AP is $0.3$ and the $2^{}\text{nd}$ term is $0.8$, find the $3^{}\text{rd}$ term. 
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