Number Sense Blog

A number is divisible by 3 if the sum of the digits is divisible by 3.   To determine if the number 87 is divisible by 3, we find the sum of its digits. Eight plus seven gives us a final sum of fifteen. Fifteen is divisible by 3. So,   ...

Recall that 1% means 1 for each 100, 1 out of 100, or one one-hundredth.   We can divide 1 by 100 to convert 1% to a decimal. 1% is equal to 0.01. Notice that dividing by one hundred moves the decimal point two places to the left.   To...

Recall that 10% means 10 for each 100, 10 out of 100, or ten one-hundredths.   We can divide 1 by 10 to convert 10% to a decimal. 10% is equal to 0.1. Notice that dividing by ten moves the decimal point one place to the left.   To find...

“Special percents” are easy to compute because they represent easy-to-calculate amounts.   0% means “none of it” 25% means “a quarter of it” 50% means “half of it” 100% means “all of it” 200% means “all of it, twice”   To f...

Here is a number sense trick to help you calculate multiplication using mental math.   We want to find the product of 5 x 4 x 3 x 2 x 1. Using our number sense, we want to find numbers close to ten or multiples of ten to make the multiplicat...