Chapter 7 Exponential and Logarithmic Functions - 7.7 Write and Apply Exponential and Power Functions - 7.7 Exercises - Skill Practice - Page 533: 9

$y=5 \times 0.5^x$

Here, we have $\dfrac{10}{b^{-1}}=a$ This gives: $a= 10 b$ $0.31 =10 b \times b^4$ Now, $0.31 =10 b^5$ This implies that $b=\sqrt [5] {0.031} =0.5$ Then, $a= 10 \times 0.5 = 5$ Hence, $y=5 \times 0.5^x$