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**rachael** 4 Joshua fell over and has a large wound on his shin. As his wound heals, the surface area of

the scab decreases. The surface area of the scab, A square centimetres, t days after the

wound was received, can be modelled by the equation A = 10 × 2−0.1t.

a What was the original surface area of Joshua’s wound?

b What is the surface area of the wound after 3 days?

c How many days after the wound was received has its surface area reduced by

i 50%? ii 95%?

d The equation for A can be re-expressed in the form A = b × e−kt, where b and k are

constants and e is the natural base.

ti Write down the value of b.

ii Find the value of k, correct to 4 decimal places.

oops... this is the question

could you help me with part d?