1. A box of thumbtacks weighed 1,590 grams. The box of thumbtacks weighed 1,470 grams after 40 thumbtacks were taken out from the box. How many thumbtacks were there in the box at first?
2. A big box can hold 12 marbles and a small box can hold 5 marbles. There are a total of 99 marbles. How many big boxes are there?
+36916 Find per unit wt of tack
(1590 - 1470) / 40 gm / tack
Now divide starting wt / unit weight to find tacks
1590 gm / [(1590 - 1470) / 40] gm/tack = 530 tacks
+36916 Here is one way start at 99 and count backwards by 5's until you hit a multiple of 12
99 - 5 = 94
94 - 5 = 89
89 - 5 = 84 Bingo ! 84/12 = 7 large boxes and 3 small boxes
But wait.... what about 24 ? then there would be 2 large boxes and 15 small boxes
