Subject :IMO Class : Class 7
A number consists of two digits whose sum is 9. If 27 is added to the number, its digits are interchanged. Given below are the steps to find the number. Identify the wrong step.
Step 1 : Let the unit’s digit be x.
Step 2 : Then, ten’s digit = (9 - x)
∴ Number = 10 × (9 - x) + x ÷ 90 - 10x + x = (90 - 9x)
Step 3 : Adding 27 to the number 90 - 9x we get 117 - 9x
Step 4 : Number with digits interchanged is 10x + (9 - x)= 9x + 9
Step 5 :127 - 9x= 9x + 9
Step 6 : Therefore unit’s digit = 6 and ten’s digit = 3
Step 7 : Hence the number = 36.
A Step 7
B Step 5
C Step 4
D Step 3 and step 6
the division sign in the number step (step before step 3) should be changedthat is the first mistake