Since multiples of 10 must be added and subtracted, focus on the number of 10s: 234 + 80 = (23 + 8) tens + 4 = 31 tens + 4 = 310 + 4 = 314 234 – 80 = (23 – 8) tens + 4 = 15 tens + 4 = 150 + 4 = 154 3 298 + 60 = 3 000 + (29 + 6) tens + 8 = 3 000 + 350 + 8 = 3 358 3 298 – 60 = 3 000 + (29 – 6) tens + 8 = 3 000 + 230 + 8 = 3 238 Rule: If multiples of 10 are added or subtracted, focus on only tens.
• 1 234 = 1 thousand + 2 hundreds + 3 tens + 4 units = 10 hundreds + 2 hundreds + 3 tens + 4 units = 12 hundreds + 3 tens + 4 units
Since multiples of 100 must be added and subtracted, focus on the number of 100s: 1 234 + 800 = (12 + 8) hundreds + 34 = 2 000 + 34 = 2 034 1 234 – 800 = (12 – 8) hundreds + 34 = 400 + 34 = 434 Rule: If multiples of 100 are added or subtracted, focus on only hundreds.
Using the inverse relationship between addition and subtraction The existence of four-fact families for addition and subtraction (refer to Number bonds) should be used to develop and reinforce this calculating strategy.
Number concept
This aspect involves counting forwards and backwards in a variety of intervals, ordering and comparing numbers, place value, odd and even numbers and multiples. Counting
The following hints should be useful: • Teach counting verbally, as well as by using apparatus like counters, counting beads, number grids, number lines (structured, semi-structured and empty), pictures that contain large numbers of objects, arrays, diagrams, Dienes’ cubes or the abacus.
• Start counting patterns at different numbers, for example, to practice counting in 4s, follow these steps: Step 1: Count from the first multiple of 4, which is 4. Step 2: Count from any other multiple of 4, e.g. 8 or 56 or 808 Step 3: Count from any other number between multiples of 4, e.g. 6 or 98 or 998 (even numbers), or 7 or 91 or 781 (odd numbers).
• Point out patterns within patterns (see table, number lines and number grids below), for example, counting in:
2s: either consecutive even or consecutive odd numbers 4s: either every second even or every second odd number 100s: only the hundreds digit change by 1.
Section 3: Teaching and learning Mathematics
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