98 Speed Math for Kids
(100 ÷ 4) 97 × 23 =
–3
–2
We divide 3 by 4 for an answer of ¾. Subtract ¾ from 23 (subtract
1 and give back ¼). We then multiply by 100.
23 – ¾ = 22¼
22¼ × 100 = 2,225 (25 is a quarter of 100)
Th e completed problem looks like this:
(100 ÷ 4) 97 × 23 = 2,225
–3
–2
- 6
-^3 / 4
2,231 Answer
You can use any combination of reference numbers. Th e general
rules are:
- Make the main reference number an easy number to multiply
by; for example, 10, 20 or 50. - Th e second reference number must be a multiple of the main
reference number; for example, double the main reference
number, or three times, ten times or fourteen times the main
reference number.
Th ere is no end to the possibilities. Play and experiment with the
methods and you will fi nd you are performing like a genius. Each
time you use these strategies you develop your mathematical skills.
Would we use two reference numbers to calculate problems such as
8 × 17 or 7 × 26? No, I think the easy way to calculate 8 × 17 is to
multiply 8 by 10 and then 8 by 7.
8 × 10 = 80
8 × 7 = 56
80 + 56 = 136