Disassembling Tens

In the pictures you can see second grade students working in groups of four: they are using Lego in order to assemble and disassemble numbers in UNITS AND TENS,

TASK 1: 

Student number 1 thinks of a number: i.e. 34

Student number 2 represents the number with Lego blocks. 

                      In this example, he needs three towers of ten  (TENS) and four units.

Student number 3 disassembles one of TENS.

Student number 4 says how many TENS and UNITS there are.

                      In this case, there are 2 TENS and 14 UNITS.

TASK 2: 

Student 1 thinks of a number with TENS and UNITS.

Student 2 thinks of another number with TEN and UNITS.

Student 3 makes the ADDITION.

                      He must bear in mind that if the number of units is bigger than ten, he will have to         assemble a new tower. 

Student 4 says the result,