Calculate s_24 for the arithmetic squence in which a_13= 1.9 and the common difference is d=3.7 a. -42.5 b. 42.6 c. -59.4 d. 1.2

D. 1.2

Step-by-step explanation:

The sum of an arithmetic sequence is the product of the average term value and the number of terms.

The average term is often computed by averaging the first and last terms of the sequence. It can also be computed by averaging the middle two terms of the sequence (when there are an even number of terms, as here).

We are given a_13 is 1.9. We know that a_12 is 3.7 less, so is -1.8. Then the average of these two middle terms is ...

... (-1.8 + 1.9)/2 = 0.05

The product of this value and the number of terms (24) is ...

... 24·0.05 = 1.2 . . . . . the sum of 24 terms of the sequence

if gloria has "carry over" minutes, (that is, any minutes paid for but not used in a month can be applied to her payment for minutes in the next month,) her total usage for the three months is: total minutes = 320 + 243 + 489 = 1052 minutes number of 200 minute blocks = 1052/200 = 5 r52 (that is 5 with a remainder of 52) rounding up the number of 200 minute blocks gives her usage for the three months as 6 blocks. the cost for six blocks is 6 x $25 = $150 she also has 200 - 52 or 148 carry over minutes if gloria pays each month and unused minutes are lost, applying the rounding up procedure to each month gives: first month usage of 320 minutes rounds up to 2 blocks of 200 minutes for a payment of 2 x $25 = $50 second month usage of 243 minutes rounds up to 2 blocks of 200 minutes for a payment of 2 x $25 = $50 third month usage of 489 minutes rounds up to 3 blocks of 200 minutes for a payment of 3 x $25 = $75 total payments for the three months are $50 + $50 + $75 = $175 get the plan with carry over minutes!