At the end of the first day, 7 weeds appear in your neighborhood park. Each day, the number of weeds increases by four times. How many weeds will be in the park at the end of 14 days?

Question

anonymous · Answer

7 weeds x 4 x 14 days

lilg132 · Answer

7 + (14 - 1) * 4

lilg132 · Answer

59 weeds in the park at the end of 14 days

anonymous · Answer

it cant be, the answer choices are 
71
626,349,395
392
35,456,231

anonymous · Answer

392 is the answer

anonymous · Answer

because 7 x 4 x 14 = 392

lilg132 · Answer

oh wait we need to work out the sum

anonymous · Answer

yeah, but im feeling there is a formula to it or something, my teacher wouldnt make it that easy

anonymous · Answer

14( 7 x 4 )

lilg132 · Answer

answer is 626349395

lilg132 · Answer

i'm not sure of the formula but what i do know is we have 7 weeds on the first day

and it multiplies by 4 each day

and you do it 14 times and add all the figures up giving you

626349395

anonymous · Answer

alright, that does make sense, thank you !

lilg132 · Answer

your welcome i will try and look for the formula for you

anonymous · Answer

thank you (:

mathmate · Answer

Use the compound interest formula:
7(4^14-1)/(4-1)=626349395
which is equivalent to
7(1+4+4^2+...4^13)

lilg132 · Answer

thats what i was looking for :)