Jamal buys 15 pencils for $0.90 each and a notebook for $1.25. the cashier says the total is $32.25, but jamal believes there was a mistake.
which equation could he use to check the reasonableness of the total?
15 × 1 + 1 = 16
15 × (1 + 1) = 30
15 × 9 + 1 = 136
15 × (9 + 1) = 150

15 × 1 + 1 = 16

Step-by-step explanation:

15 pencils for $0.90 = 15*.90

1 notebook for 1.25 = 1*1.25

Add them together

15*.90+1*1.25

We can round .90 to 1 dollar an 1.25 to 1 dollar

15*1 + 1*1

15+1 =16

29.5977692753

step-by-step explanation:

the largest number of the four options is 1.8 x 10-2

you have it in scientific notation.

1.80 x 10-6   = 0.00000180

1.80 x 10-4   = 0.000180 (bigger, or "less small", than the former one)

so

1.8 x 10-2       = 0.0180. as you see. the "less small", or the biggest one of them all.

as you have negative exponent, it means you are dividing 1.8 by 100 (i.e. moving the dot towards left, two times).

if you had positive exponent for the scientific notation, power of tenths, you would be multiplying times 100 (moving the dot towards right) as below:

1.8 x (10)2 = 180

so. if you have negative exponent in scientific notation, move the dot toward left. if it is positive, toward right as many times the exponent tells you.