Question

A collection of dimes is arranged in a triangular array with 18 coins in the base row, 17 in the next, 16 in the next, and so forth with 1 dime in the last row. Find the value of the collection.

Answer 1

first find num of dimes then multiply by 0.1 to get value in dollars
sequence goes 18,17,16...1
so you are subtracting 1 each time
there is a formula for sum of arithmetic sequence
sum = 1/2*n*(a1+an)
n=num of rows

Answer 2

im still a little lost

Answer 3

ok just concentrate on the formula for the sum of the series
we need a value for n, a1, and an
n is num of rows
a1 is first num in sequence
an is last num in sequence

Answer 4

hmmmm

Answer 5

whats first num in sequence

Answer 6

how many dimes in first row?
how many dimes in last row?

Answer 7

still lost?
ok top row has one dime
bottom row has 18 dimes
since each row has one more than prev row
there are a total of 18 rows
1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18
sum = 1/2*18*(1+18)
sum = 1/2*18*19
sum = 9*19
sum = 171
171 dimes = 17.10 in dollars

Answer 8

ah ok got it... thank you!!!

Answer 9

no prob