a boy is building a pyramid out of building blocks. he put 20 blocks in the first row, then he puts 19 blocks in the row above, and so on. find the total number of blocks he needs. find the total number of blocks he need

Consider a bag that contains 220 coins of which 6 are rare indian pennies. for the given pair of events a and b, complete parts (a) and (b) below. a: when one of the 220 coins is randomly selected, it is one of the 6 indian pennies. b: when another one of the 220 coins is randomly selected (with replacement), it is also one of the 6 indian pennies. a. determine whether events a and b are independent or dependent. b. find p(a and b), the probability that events a and b both occur.

If tan2a=cot(a+60), find the value of a, where 2a is an acute angle

The angles in a triangle are represented by 5x, 8x, and 2x+9. what is the value of ? a.10.8 b.11.4 c.9.7 d.7.2