Question

Mr.Burn's class is taking aa field trip to the planetatium. The trip will $27 for each student. There are 18 students in his class . Use compatible numbers to estimate the total cost of the field trip

Answer 1

27*18 = 486
The trip should cost around $486.

Answer 2

$27 x 18 students = 486 actual cost.

$30 x 10 students = 300 estimated total cost using compatible numbers.
$20 x 20 students = 400 estimated total cost using compatible numbers. (better option because it is nearer to the actual cost)

Compatible numbers are numbers that can easily be multiplied or divided using mental computation.

Compatible number for 27 and 18 can be: 30 and 20 OR 20 and 20 OR 30 and 10 OR 20 and 10.

However, there is a rule in multiplying the compatible numbers, when one number is increased the other number must be decreased.

So 27 can be increased to 30; while 18 can be decreased to 10 to get a product of 300.

27 can be decreased to 20; while 18 can be increased to 20 to get a product of 400.