The schools book store ordered three - ring notebooks. they put 75% of the order in the warehouse and sold 80% of the rest in the first week of school. there are 25 notebooks left in the store to sell. how many 3- ring notebooks did they originally order?

Ok so x + y = n (where n is the number of the original order, x is the part that went to the store and y is the number in the warehouse.)

25 = 20% of x, so x = (25 divided by .2) = 125 notebooks went to the store.

125 = 25% of total n (because 75% went into warehouse and 100-75 = 25).

so 125 divided by .25 = 500 notebooks. total.

and (500-125 = 375 notebooks into the warehouse.)

D. triangular pyramid