Let x be the number of $5 items sold. Let y be the number of $25 items sold. x + y = 150 x = 150 - y .........(1) 5x + 25y = 1950 ......(2) Plugging the expression for x from (1) into (2), we get: 5(150 - y) + 25y = 1950 750 - 5y + 25y = 1950 20y = 1200 y = 60 items. The answer is, there were 60 items sold at $25.
These concepts become more clear when teachers use number disks instead of base ten blocks. Place value is a very important concept for elementary students because base ten is the foundation of our number system.
