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Algebra Level 2

11 × 11 = 121 11 × 22 = 242 11 × 33 = 363 11 × 54 = 594 11 × 99 = ? 11 \times 11 = 121\\11 \times 22 = 242\\11 \times 33 = 363\\11 \times 54 = 594\\11 \times 99 = ?

what is the answer to 11 × 99 11 \times 99 ?

9819 9279 9189 1089

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2 solutions

Jayden Kallusky
Jan 25, 2016

The Trick

You have to add the two digits which aren't the 11's together and write your answer between your two digits (ex: 11 x 22 = 242 because you add 2 add 2 together and put 4 between 2 and 2).

In the problem your answer would be 1089 instead of 9189 because you have to carry. First add 9 and 9 together and your answer is 18. Like you were taught back in grade one and two you have to remember to carry. Like before you have to put your 18 between the two 9's. However, this time you have to add your 1 and 9 together. so your answer becomes 1089. Always remember to add your two left digits together when multiplying 11 by a two digit number and the the sum of those two digits result in another two digit number.

(hope this visual helps)

see if you get this one? 11 x 78

(the answer is 858)

Good...But i actually did it in 2 seconds using mental calculation 😜

Anuj Shikarkhane - 5 years, 4 months ago

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Yea. 990 + 99.

Arulx Z - 5 years, 4 months ago

Nice solution!

A Former Brilliant Member - 5 years, 4 months ago
Mohammad Khaza
Jul 23, 2017

at first ,99 x 10 = 990 990

now, 990+99 =1089

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