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what is the first 50 terms of a pattern sum to 2000?

 Sep 28, 2014

Best Answer 

 #1
avatar+23248 
+5

One way to do this that will work for other questions of this type (that is, for other number of terms and for other sum) is the following (but it won't by a 'pretty' answer:

Since we want 50 terms, add the first 50 whole numbers: 1 + 2 + 3 + ... + 48 + 49 + 50.

There is a formula that allows you do add these quickly: n = number of terms, f = first term, l = last term:

     Sum = n(f+l)/2

Since n = 50, first = 1, and last = 50:     Sum = 50(1+50)/2  --->  Sum = 50(51)/2  ---> Sum =1275

But the sum is 1275 and we want a sum of 2000, we need to 'scale up' every number.

How much? Since we want 2000 and not 1275, the scale factor will be 2000/1275 or 80/51.

Let's multiply each term by 80/51; this will then multiply the answer by 80/51 (and 80/51 x 1275 = 2000).

The terms are 1(80/51) + 2(80/51) + 3(80/51) + ... + 48(80/51) + 49(80/51) + 50(80/51)

or: 80/51 + 160/51 + 240/51 + ... + 3840/51 + 3920/51 + 4000/51

 Sep 28, 2014
 #1
avatar+23248 
+5
Best Answer

One way to do this that will work for other questions of this type (that is, for other number of terms and for other sum) is the following (but it won't by a 'pretty' answer:

Since we want 50 terms, add the first 50 whole numbers: 1 + 2 + 3 + ... + 48 + 49 + 50.

There is a formula that allows you do add these quickly: n = number of terms, f = first term, l = last term:

     Sum = n(f+l)/2

Since n = 50, first = 1, and last = 50:     Sum = 50(1+50)/2  --->  Sum = 50(51)/2  ---> Sum =1275

But the sum is 1275 and we want a sum of 2000, we need to 'scale up' every number.

How much? Since we want 2000 and not 1275, the scale factor will be 2000/1275 or 80/51.

Let's multiply each term by 80/51; this will then multiply the answer by 80/51 (and 80/51 x 1275 = 2000).

The terms are 1(80/51) + 2(80/51) + 3(80/51) + ... + 48(80/51) + 49(80/51) + 50(80/51)

or: 80/51 + 160/51 + 240/51 + ... + 3840/51 + 3920/51 + 4000/51

geno3141 Sep 28, 2014

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