Round off the following numbers to the nearest 100 and perform the calculations: a) 287, b) 765, c) 423, d) 1392, e) 342, f) 550. Also, calculate: a) 16x17, b) 21x51, c) 43x25, d) 30x29, e) 38x17.

Here are the solutions to your problems:

1. Round off to the nearest 100

• a) 287 The tens digit is 8, which is 5 or greater, so round up the hundreds digit. $$287 \approx \boxed{300}$$
• b) 765 The tens digit is 6, which is 5 or greater, so round up the hundreds digit. $$765 \approx \boxed{800}$$
• c) 423 The tens digit is 2, which is less than 5, so keep the hundreds digit the same. $$423 \approx \boxed{400}$$
• d) 1392 The tens digit is 9, which is 5 or greater, so round up the hundreds digit. $$1392 \approx \boxed{1400}$$
• e) 342 The tens digit is 4, which is less than 5, so keep the hundreds digit the same. $$342 \approx \boxed{300}$$
• f) 550 The tens digit is 5, which is 5 or greater, so round up the hundreds digit. $$550 \approx \boxed{600}$$

2. Calculation

• a) Example: $16 \times 17$ $$16 \times 17 = \boxed{272}$$
• b) $21 \times 51$