According to the sum of n terms in geometric progression, the total time she took to complete her first five homework assignments is 219 minutes.
The time taken to complete first assignment is 70 minutes.
She takes 0.8 times as long to complete each homework assignment as she took to complete the preceding assignment.
This shows that the given series is in geometric progression, where
a = first term = 70
r = common ratio = 0.8
The sum of first n terms in geometric progression is given by,
Sₙ = a (rⁿ - 1) / r - 1
S₅ = 70 (0.8⁵ - 1) / 0.8 - 1
S₅ = 219
Therefore, the total time she took to complete her first five homework assignments is 219 minutes.
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