COMBINATORICS There are 15 pupils who enjoy solving puzzles. They meet each other to solve puzzles. At their first meeting, they shake hands with each other. Find the number of handshakes if
(a) all shake hands with one another,

(b) three people who know one another do not shake hands with each other.​

Jenisey has $24 to spend on seven pencils. after buying them she had $10. how much did each pencil cost.?

Each of the following data sets has a mean of x = 10. (i) 8 9 10 11 12 (ii) 7 9 10 11 13 (iii) 7 8 10 12 13 (a) without doing any computations, order the data sets according to increasing value of standard deviations. (i), (iii), (ii) (ii), (i), (iii) (iii), (i), (ii) (iii), (ii), (i) (i), (ii), (iii) (ii), (iii), (i) (b) why do you expect the difference in standard deviations between data sets (i) and (ii) to be greater than the difference in standard deviations between data sets (ii) and (iii)? hint: consider how much the data in the respective sets differ from the mean. the data change between data sets (i) and (ii) increased the squared difference îł(x - x)2 by more than data sets (ii) and (iii). the data change between data sets (ii) and (iii) increased the squared difference îł(x - x)2 by more than data sets (i) and (ii). the data change between data sets (i) and (ii) decreased the squared difference îł(x - x)2 by more than data sets (ii) and (iii). none of the above

Of of at a : $6, $8, $7, $6, $5, $7, $5, $7, $6, $28, $30 is?ato .ato .ato .ato .