Example 1 - Australian Teacher

Speedy Maths- for ages 10 and up -Solutions are in red. Teachers maychoose to remove solutions andthen print for student use.© Australian Teacher1

Speedy MathsMultiplying Two Digit Numbers by 11The first step is to write the number, leaving some space between thetwo digits.Then insert the sum of the number’s two digits in between the two digitsthemselves; you will have to carry when the sum of the digits exceeds 9.Example 1: 36 x 11 Example 2: 78 x 11.1) 3 62) 3+6=93) 3961) 7 82) 7+8=153) 858Challenge:How fast can you do these?1) 25 x 11 2752) 42 x 11 4623) 72 x 11 7924) 34 x 11 3745) 26 x 11 2866) 84 x 11 9247) 76 x 11 8368) 97 x 11 1 0679) 67 x 11 73710) 46 x 11 506Use the same method but work backwards:11) ? x 11 = 396 3612) ? x 11 = 781 7113) ? x 11 = 187 1714) ? x 11 = 385 3515) ? x 11 = 484 4416) ? x 11 = 748 6817) ? x 11 = 209 1918) ? x 11 = 638 5819) ? x 11 = 858 7820) ? x 11 = 1 078 98---------------------------------------© Australian Teacher2

Speedy MathsSquaring Two Digit Numbers ending in 5To square a number ending in 5, first multiply thenumber formed by the digit(s) in front of the 5 by thenext whole number. To that product, affix the number25. The number to affix (25) is easy to remember, because5 2 = 25.Example 1: How much is 25 2 ?2 x 3 = 6 Write down 6 and affix 25… = 625Example 2: How much is 75 2 ?7 x 8 = 56 Write down 56 and affix 25… = 5 625Challenge:1. How much is 85 2 – 35 2 ? 7225 – 1225 = 6 0002. How much is 45 2 + 95 2 ? 2025 + 9025 = 11 0503. How much is 115 2 ? (use same method) 11 x 12 = 132; so 115 2 = 13 2254. How much is 195 2 ? 19 x 20 = 380; so 195 2 = 38 0255. How much is 2 995 2 ? 299 x 300 = 89 700; so 2 995 2 = 8 970 025-----------------------------------------------© Australian Teacher3