The basics of the concept of REMAINDER... I show with visual models how divisions are not always even (not exact), and we have a remainder. For example, I divide 15 into groups of 4. We get three groups, and three left over: 15 ÷ 4 = 3 R3.
After working with visual models, I explain how you can calculate the remainder. For example, to solve 24 ÷ 5, think how many 5's are there in 24. There are four, because 4 × 5 = 20, but 5 × 5 = 25, which is too much (more than 24). Then we look at the DIFFERENCE of 4 × 5 and 24, which is 4, and that is the remainder.
Lastly you get to practice on your own (pause the video) with some exercise problems, and with a pattern. The pattern shows us that as we increase the dividend by one (keeping the divisor the same), the remainder also increases by one... until you come to the next even division.
Division with remainders (mental math) — online practice
Division word problems versus multiplication word problems
Math Mammoth Grade 3 curriculum