"\\text {Let b is a constant, then}\\\\\nf(t)=b[(t+10)-2]=b(t+8), 0<t<40\\\\\nb\\int _0^{40}(t+8)dt=1\\\\\nb\\left[\\frac{t^2}{2}+8t\\right]^{40}_0=1\\\\\nb[\\frac{40^2}{2}+8(40)]=1\nb(1120)=1\\\\\n\\therefore b=\\frac{1}{1120}\\\\\nP(t<10)=\\frac{1}{1120}\\int _0^{10}t+8dt\\\\\n=\\frac{1}{1120}\\left[\\frac{t^2}{2}+8t\\right]^{40}_0\\\\\n=\\frac{1}{1120}[\\frac{10^2}{2}+8(10)]\\\\\n=\\frac{1}{1120}\\times 130\\\\\n=\\frac{13}{112}"
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