Estimate each of the following by rounding off each number to nearest tens:
(a) 11963 – 9369
(b) 76877 – 7783
(c) 10732 – 4354
(d) 78203 – 16407
(a) 11960 – 9370 = 2590
(b) 76880 – 7780 = 69100
(c) 10730 – 4350 = 6380
(d) 78200 – 16410 = 61790
Idea: Round each number to the nearest ten, then subtract.
Rounding rule: Look at the ones digit.
• If ones digit is 0–4 → round down to the previous ten.
• If ones digit is 5–9 → round up to the next ten.
(a) 11963 – 9369
11963 → ones digit = 3 → round down: \(11963 \to 11960\).
9369 → ones digit = 9 → round up: \(9369 \to 9370\).
Now subtract:
\(11960 - 9370 = 2590\).
(b) 76877 – 7783
76877 → ones digit = 7 → round up: \(76877 \to 76880\).
7783 → ones digit = 3 → round down: \(7783 \to 7780\).
Now subtract:
\(76880 - 7780 = 69100\).
(c) 10732 – 4354
10732 → ones digit = 2 → round down: \(10732 \to 10730\).
4354 → ones digit = 4 → round down: \(4354 \to 4350\).
Now subtract:
\(10730 - 4350 = 6380\).
(d) 78203 – 16407
78203 → ones digit = 3 → round down: \(78203 \to 78200\).
16407 → ones digit = 7 → round up: \(16407 \to 16410\).
Now subtract:
\(78200 - 16410 = 61790\).