Kelly has driven by Ryan's house 3 times a day for the past 6 weeks. Every time she drives by, she leaves 2 love letters on his porch. Ryan has thrown out 90% of the
letters and a dog ran away with 5% of them. Ryan secretly keeps the rest in his
Memories Box. How many letters does he have in his box?

There are 13 letters in his box

Explanation:

Given

Duration = 6 weeks

Letters = 2 per trip

Required

Determine the number of letters with Ryan

First, we need to calculate the duration in days

Duration = 6 weeks

Duration = 6 * 7 days

Duration = 42 days

Next, we need to determine the number of trips

Trips = 3 times a day

So: In 42 days, the trip will be

Trip = 3 * 42

Trip = 126

Next, we need to calculate the number of letters delivered

Letters = 2 per trip

So: In 126 trips, the letters will be

Letters = 2 * 126

Letters = 252

At this point, we can now calculate the number of letters in his memory box.

First, we need to determine the percentage left with him

%Left = 100% - %Thrown Away - %Snatch by Dogs

%Left = 100% - 90% - 5%

%Left = 5%

The number of letters left is:

Numbers = %Left * Letters

Numbers = 5% * 252

Numbers = 12.6

Numbers = 13 (Approximated)

Hence, there are 13 letters in his box

see below  

explanation:

all of the above