Mentally add a multiple of 10 (e.g., 20, 50) to a 3-digit number without crossing the hundreds boundary (e.g., 325+40). May 13, 2025 by Dan
Mentally subtract a single-digit number from a 3-digit number crossing the hundreds boundary (e.g., 503−7). May 13, 2025 by Dan
Mentally subtract a single-digit number from a 3-digit number crossing the tens boundary (e.g., 452−5). May 13, 2025 by Dan
Mentally subtract a single-digit number from a 3-digit number without crossing the tens boundary (e.g., 456−3). May 13, 2025 by Dan
