1. **Complete Number Walls:** The rule is each number above equals the sum of the two below it. For bottom row 13,18,23: Middle row: 13+18=31, 18+23=41 Top: 31+41=72 Completed pyramid: 72 31 41 13 18 23 For bottom row 31,29,17: Middle row: 31+29=60, 29+17=46 Top: 60+46=106 Completed pyramid: 106 60 46 31 29 17 For bottom row 25,37,32: Middle row: 25+37=62, 37+32=69 Top: 62+69=131 Completed pyramid: 131 62 69 25 37 32 For bottom row 48,28,19: Middle row: 48+28=76, 28+19=47 Top: 76+47=123 Completed pyramid: 123 76 47 48 28 19 2. **Calculate 786 + 498:** Add the ones: 6 + 8 = 14, write 4 and carry 1. Add the tens: 8 + 9 = 17 plus 1 carried = 18, write 8 and carry 1. Add the hundreds: 7 + 4 = 11 plus 1 carried = 12. Final sum is 1284. 3. **Efficient addition and subtraction:** a) 543 + 219 = 762 b) 543 - 219 = 324 Final answers: Number walls top numbers: 72, 106, 131, 123 Sum 786 + 498 = 1284 a) 543 + 219 = 762 b) 543 - 219 = 324