Two quantities

In Primary 2, you learned that 3 times 4 means 3 groups of 4. 3 groups of 4 make 12. Today, we will draw bars of equal units and find the value of one unit. Mei and Kavin collected 36 shells altogether. Mei collected 3 times as many shells as Kavin. How many shells did Mei collect? Mei collected 3 times as many shells as Kavin. So Kavin's shells make 1 unit. Every unit we draw is this same size. Mei's bar is 3 of these units. One unit, two units, three units. Together, they collected 36 shells. The question asks for Mei's shells. The 36 shells cover both bars, so we count all the units. Mei has 3 units and Kavin has 1 unit. 3 units plus 1 unit is 4 units. So 4 units make 36 shells. To find 1 unit, we share 36 equally among the 4 units. 36 divided by 4 is 9. So each unit is 9 shells. Mei has 3 units. 3 times 9 is 27. So Mei collected 27 shells.

Siti and Bala have 40 shells altogether. Siti has 4 times as many shells as Bala. How many shells does Siti have? Try it first. Pause if you like. Siti has 4 times as many shells as Bala, so Bala's shells make 1 unit. So Siti's bar is 4 of these units. Together, they have 40 shells. The question asks for Siti's shells. 4 units plus 1 unit is 5 units. So 5 units make 40 shells. 40 divided by 5 is 8. So each unit is 8 shells. Siti has 4 units. 4 times 8 is 32. So Siti has 32 shells.

Ravi has 5 times as many shells as Wei Jie. Ravi has 28 more shells than Wei Jie. How many shells does Wei Jie have? Try it first. Pause if you like. Ravi has 5 times as many shells as Wei Jie, so Wei Jie's shells make 1 unit. So Ravi's bar is 5 of these units. Ravi's first unit is the same as Wei Jie's unit. So Ravi's other units are the 28 more shells. The question asks for Wei Jie's shells. 5 units minus 1 unit is 4 units. So 4 units make 28 shells. Wei Jie has just 1 unit. 28 divided by 4 is 7. So Wei Jie has 7 shells. Count the units under the number you know. Then find one unit, and use it to answer the question.