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# C1 help ! watch

1. Basically i need help with my hw which is due tomz. i really dont understand it. the topic is on arithmetic series so i would appreciate it if you helped it me out.

1) A girl saves money over a period of 200 weeks. She saves 5p in week 1, 7p in week2, 9p in week 3, and so on until week 200. her weekly savings form an arithmetic sequence.

a)find the amount she saves in week 200

b)calculate her total savings over the completer 200 week period

thank you.

2. a1 is 5. Our common difference is 2. n is 200. Shove the numbers in and out will come the answer.

Now do it with this formula to find the sum.

You just have to learn these formulas tbh, there's not that much understanding to be done.
3. (Original post by SpringNicht)

a1 is 5. Our common difference is 2. n is 200. Shove the numbers in and out will come the answer.

Now do it with this formula to find the sum.

You just have to learn these formulas tbh, there's not that much understanding to be done.
so a is 5 and d is 2. thank you so much btw 1!!
4. To answer questions involving arithmetic series in C2, you need to know two formulas:

One formula calculates the nth term : Un=a+(n-1)d , where a is the first term (5), d is the difference (2) and n is the term with unknown value (200)

There is another formula: Sn=1/2n[2a+(n-1)d] calculates the the sum of the terms up to term n. Sn is the sum to n terms, and then like before a is the first term, d is the difference and n is the term with unknown value. Again, it is literally a case of substituting values for letters and calculating.
5. basically im struggling with this question and i would appreciate it if one of you helped me out !

1) An athlete prepares for a race by competing a practice run on each of 11 consecutive days.On each day after the first day he runs further than he ran on the previous day. The lengths of his 11 practice runs form an arithmetic sequence with first term (a) km and common difference (d) km.

he runs 9 km on the 11th day and he runs a total of 77km over the 11 day period.

find the value of a and d.
6. you know a+10d
And you know 11/2(2a +10d)

So you solve the simultaneous equations

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