Determine AP

Determine the difference of the arithmetic progression if a3 = 7, and a4 + a5 = 71

Correct answer:

d =  19

Step-by-step explanation:

$$\begin{gathered} a_3=7 \\ {a}_4+a_5=71 \\ {a}_3+d+a_3+2d=71 \\ 2a_3+3d=71 \\ d=(71-2\cdot a_3)\mathrm{/}3=(71-2\cdot 7)\mathrm{/}3=19 \end{gathered}$$

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