Challenging sums

[ccyy1993]

Q1. If numbers are arranged in 3 rows A, B, C according to the following table, which row will contain the number 1000?

A : 1, 6, 7, 12, 13, 18, 19.................
B: 2, 5, 8, 11, 14, 17, 20.................
C: 3, 4, 9, 10, 15, 16, 21.................

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Q2. 2004 students arrange themselves in a row. In the first round of counting, they number themselves:

1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3,.........................................
FROM LEFT TO RIGHT.

In the second round of counting, they number themselves:

1,2,3,4,5,1,2,3,4,5,1,2,3,4,5,...............................................
FROM RIGHT TO LEFT.

Find the number of students whose SUM OF NUMBERS IN THE FIRST AND SECOND ROUNDS of counting is 5.

[Mat_D]

Q1 answer is row C

[burnhal]

stab at 402 for the last Q- three in every fifteen and also three in the last 9??

[Mat_D]

Q2 answer is 401

1 2 3 1 2 3 1 2 3 1 2 3 1 2 3

1 2 3 4 5 1 2 3 4 5 1 2 3 4 5

This sequence repeats every 15 pupils

There are 3 pupils in this sequence that add up to 5

at position 4, 8 and 13

2004 / 15 = 133.6

133 x 3 = 399

That leave 0.6 (or 60%) of the sequence.

15 x 0.6 = 9

there are 2 pupils that add up to 5 in the first 9

399 + 2 = 401

QED 

[burnhal]

take a closer look at the question- one lot is numbered left to right and the next time its right to left!!!!

[burnhal]

so take your fifteens from the right hand side of the line- its positions 7,8 and 9 counting from the right

[Mat_D]

Ooops...Didn't spot that.

The answer is 402, your'e right.

Pupils at positions 7,8,9 !!!

must read the question must read the question must...

[ccyy1993]

Does anyone know the answer to question 1?

[ccyy1993]

How do you get the answer to Q1??