Mental addition and subtraction by adjusting (99, 199, 101…)

Question 1

381 + 99 = ?

Answer 

Question 2

Diego works out 713 − 99 by doing 713 − 100 = 613, then subtracting 1 more to get 612. What should Diego have done, and what is 713 − 99?

Answer 

Question 3

204 + 99 = ?

Answer 

Question 4

Hiro works out 457 − 99 by doing 457 − 100 = 357, then subtracting 1 more to get 356. What should Hiro have done, and what is 457 − 99?

Answer 

Question 5

243 + 99 = ?

Answer 

Question 6

Grace works out 719 − 99 by doing 719 − 100 = 619, then subtracting 1 more to get 618. What should Grace have done, and what is 719 − 99?

Answer 

Question 7

194 + 201 = ?

Answer 

Question 8

Mei works out 585 − 99 by doing 585 − 100 = 485, then subtracting 1 more to get 484. What should Mei have done, and what is 585 − 99?

Answer 

Question 9

292 − 98 = ?

Answer 

Question 10

Ravi works out 707 − 99 by doing 707 − 100 = 607, then subtracting 1 more to get 606. What should Ravi have done, and what is 707 − 99?

Answer 

Question 11

526 − 299 = ?

Answer 

Question 12

Zara works out 346 − 99 by doing 346 − 100 = 246, then subtracting 1 more to get 245. What should Zara have done, and what is 346 − 99?

Answer 

Question 13

373 + 201 = ?

Answer 

Question 14

Mateo works out 382 − 99 by doing 382 − 100 = 282, then subtracting 1 more to get 281. What should Mateo have done, and what is 382 − 99?

Answer 

Question 15

480 − 201 = ?

Answer 

Question 16

Kwame works out 373 − 99 by doing 373 − 100 = 273, then subtracting 1 more to get 272. What should Kwame have done, and what is 373 − 99?

Answer