Answer/Step-by-step explanation:
The basic rule of maths operation used by Sandi, is the PEMDAS Rule.
Maths operations like the one Sandi was given must follow this rule. According to the rule:
P - Parentheses, solve everything you have in the parentheses first.
E - Exponents, do the exponents.
M - Multiplication or
D - Division operation should come next.
A - Addition or
S - Subtraction comes last.
Let's apply this rule to see if Sandi rightly applied the PEMDAS Rule:
Step 1:
6*4 + 2 ÷ 2 - 7 (given)
Step 2: perform operation involving Multiplication first according to PEMDAS Rule.
24 + 2 ÷ 2 - 7 (multiplication first. I.e. 6*4 = 24)
Step 3: perform division operation next.
24 + 1 - 7 (division operation. i.e. 2÷2 = 1)
Step 4: Subtraction
24 - 6 (i.e. +1 - 7 = -6) this is where Sandi made an error.
Step 5: subtraction
24 - 6 = 18.
Sandi made a mistake in step 4 and 5. Her addition and subtraction operation was wrong. 1 - 7 = -6 not +6.
During operation like this, either subtraction or addition can come first.
