Michelle and Natasha each had to repair their new iPhones. The initial cost of each repair is $100. Michelle and Natasha each have two discount coupons. Each of them uses both coupons toward the cost of the repair. One coupon is for $25 off the repair cost and the other coupon is for 20% off the repair cost.
Michelle and Natasha use their coupons in a different order, as shown below.
Michelle uses the 20% off the repair cost coupon first. She then uses the $25 off the repair cost coupon on the remaining balance.
Natasha uses the $25 off the repair cost coupon first. She then uses the 20% off the repair cost coupon on the remaining balance.
n

  about 5.6 days

step-by-step explanation:

we can fill the given information into the decay equation and solve for the value of t at which half the sample remains.

the half-life is about 5.6 days.

3. parallelogram

step-by-step explanation:

we turn each of our sides into direction vectors

ab=b-a=(3 - 7, 1 - 0) = (-4, 1)

bc=c-b=(1,6)

cd=d-c=(4,-1)

da=a-d=(-1,-6)

we see how the opposite sides have negated direction vectors; this is characteristic of a parallelogram.   we have congruent sides ab=cd and bc=da with unequal lengths because 1^2+6^2 is different from (-4)^2+1^2.   so it's not a square or a rhombus.  

we check the dot product of direction vectors of adjacent sides.   we have

ab dot bc = -4(1) + 1(6) = 2

that's not zero so the sides are not perpendicular.   we've ruled out rectangle.

the direction vectors indicate two pairs of congruent parallel sides, so we choose parallelogram over trapezoid.

step-by-step explanation:

circumference divided by 3.141592654 then timesthe radius twice